Try this: https://sogo.nu/nc/support/faq/article/how-do-i-debug-sogo.html

Here's the output from gdb

(gdb) bt
#0 __GI_abort () at abort.c:51
0000001 0x000055555555c5eb in -[SOGo handleException:inContext:] (self=<optimized out>, _cmd=<optimized out>, _exc=<optimized out>, _ctx=<optimized out>)
at SOGo.m:449
0000002 0x00007ffff6c8ef4d in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000003 0x00007ffff6c5633c in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000004 0x000055555555c99e in -[SOGo dispatchRequest:] (self=0x5555558b7ac0, _cmd=<optimized out>, _request=0x5555560f10c0) at SOGo.m:565
0000005 0x00007ffff6ce99fd in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000006 0x00007ffff6ceaec8 in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000007 0x00007ffff6ce5f5a in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000008 0x00007ffff6ce6da6 in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000009 0x00007ffff6ce713a in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000010 0x00007ffff6ce71c4 in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000011 0x00007ffff5456d07 in ?? () from /usr/lib/libgnustep-base.so.1.24
0000012 0x00007ffff5561b3b in ?? () from /usr/lib/libgnustep-base.so.1.24
0000013 0x00007ffff549f840 in ?? () from /usr/lib/libgnustep-base.so.1.24
0000014 0x00007ffff549fcf2 in ?? () from /usr/lib/libgnustep-base.so.1.24
0000015 0x00007ffff6c5771e in ?? () from /usr/lib/libNGObjWeb.so.4.9
0000016 0x000055555555c2bf in -[SOGo run] (self=0x5555558b7ac0, _cmd=<optimized out>) at SOGo.m:326
0000017 0x00007ffff6c7bf54 in WOApplicationMain () from /usr/lib/libNGObjWeb.so.4.9
0000018 0x00007ffff6c97c8f in WOWatchDogApplicationMain () from /usr/lib/libNGObjWeb.so.4.9
0000019 0x000055555555a7ab in main (argc=13, argv=0x7fffffffec58, env=<optimized out>) at sogod.m:51

This not useful, reread the documentation.

You mean there were some more *-dbg packages missing..

#0 -[NSException raise] (self=0x55555629a4b0, _cmd=0x7ffff58fcfc0 <_OBJC_SELECTOR_TABLE+384>) at NSException.m:960
0000001 0x00007ffff54137a3 in +[NSException raise:format:] (self=0x7ffff58fd2c0 <_OBJC_Class_NSException>, _cmd=<optimized out>,
name=0x7ffff58fd950 <_OBJC_INSTANCE_4>, format=0x7ffff592c7b0 <_OBJC_INSTANCE_10>) at NSException.m:840
0000002 0x00007ffff54677f6 in -[NSObject doesNotRecognizeSelector:] (self=0x555555ea1b60, _cmd=<optimized out>, aSelector=<optimized out>) at NSObject.m:1765
0000003 0x00007ffff5527fd3 in GSFFIInvocationCallback (cif=0x55555629a4b0, retp=0x7fffffffba40, args=0x55555629c9f0, user=0x55555629cbc0)
at GSFFIInvocation.m:629
0000004 0x00007ffff18b1baf in ffi_closure_unix64_inner () from /usr/lib/x86_64-linux-gnu/libffi.so.6
0000005 0x00007ffff18b1f28 in ffi_closure_unix64 () from /usr/lib/x86_64-linux-gnu/libffi.so.6
0000006 0x00007fffe984d6cb in -[UIxCalendarSelector calendars] (self=0x55555614fd30, _cmd=<optimized out>) at UIxCalendarSelector.m:167
0000007 0x00007ffff6ca4bd5 in _getComponentValue (self=self@entry=0x55555620b8e0, object=0x55555614fd30, info=info@entry=0x555556153c90)
at WOKeyPathAssociation.m:537
0000008 0x00007ffff6ca9080 in _getValueN (root=<optimized out>, _count=2, self=0x55555620b8e0) at WOKeyPathAssociation.m:737
0000009 _getValue (root=<optimized out>, self=0x55555620b8e0) at WOKeyPathAssociation.m:750
0000010 -[WOKeyPathAssociation valueInComponent:] (self=0x55555620b8e0, _cmd=<optimized out>, _component=<optimized out>) at WOKeyPathAssociation.m:1004
0000011 0x00007ffff6cd8e53 in -[_WOComplexString appendToResponse:inContext:] (self=0x55555607c840, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOString.m:561
0000012 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x5555561541f0, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000013 0x00007ffff6cc8c07 in -[WOGenericContainer appendToResponse:inContext:] (self=0x55555616ba60, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOGenericContainer.m:121
0000014 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x55555611ee10, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000015 0x00007ffff6c5c3d2 in -[WOComponent appendToResponse:inContext:] (self=0x55555614fd30, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOComponent.m:928
0000016 0x00007ffff6c7c887 in -[WOChildComponentReference appendToResponse:inContext:] (self=0x555555f7c2a0, _cmd=0x7ffff6fe9950 <_OBJC_SELECTOR_TABLE+720>,
_response=0x555555f968e0, _ctx=0x555555f5d3d0) at WOChildComponentReference.m:181
0000017 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x5555562182a0, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000018 0x00007ffff6cc1001 in -[WOComponentContent appendToResponse:inContext:] (self=<optimized out>, _cmd=0x7ffff6fe9950 <_OBJC_SELECTOR_TABLE+720>,
_response=0x555555f968e0, _ctx=0x555555f5d3d0) at WOComponentContent.m:149
0000019 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x5555560a7c10, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000020 0x00007ffff6cc39d0 in -[WOConditional appendToResponse:inContext:] (self=<optimized out>, _cmd=<optimized out>, _response=0x555555f968e0,
---Type <return> to continue, or q <return> to quit---
_ctx=0x555555f5d3d0) at WOConditional.m:242
0000021 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x555556071200, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000022 0x00007ffff6cbd394 in -[WOBody appendToResponse:inContext:] (self=<optimized out>, _cmd=<optimized out>, _response=0x555555f968e0, _ctx=0x555555f5d3d0)
at WOBody.m:157
0000023 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x55555618f740, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000024 0x00007ffff6cc8c07 in -[WOGenericContainer appendToResponse:inContext:] (self=0x555555f8e390, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOGenericContainer.m:121
0000025 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x555555f91760, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000026 0x00007ffff6cc39d0 in -[WOConditional appendToResponse:inContext:] (self=<optimized out>, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOConditional.m:242
0000027 0x00007ffff6cc29a2 in -[WOCompoundElement appendToResponse:inContext:] (self=0x555555eb3960, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOCompoundElement.m:247
0000028 0x00007ffff6c5c3d2 in -[WOComponent appendToResponse:inContext:] (self=0x555556054500, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOComponent.m:928
0000029 0x00007ffff6c7c887 in -[WOChildComponentReference appendToResponse:inContext:] (self=0x555556218240, _cmd=0x7ffff6fc91a0 <_OBJC_SELECTOR_TABLE+352>,
_response=0x555555f968e0, _ctx=0x555555f5d3d0) at WOChildComponentReference.m:181
0000030 0x00007ffff6c5c3d2 in -[WOComponent appendToResponse:inContext:] (self=0x55555623ceb0, _cmd=<optimized out>, _response=0x555555f968e0,
_ctx=0x555555f5d3d0) at WOComponent.m:928
0000031 0x00007ffff6cf12eb in -[SoDefaultRenderer renderComponent:inContext:] () from /usr/lib/libNGObjWeb.so.4.9
0000032 0x00007ffff6cf8412 in -[SoObjectRequestHandler renderObject:inContext:] () from /usr/lib/libNGObjWeb.so.4.9
0000033 0x00007ffff6cf8f6d in -[SoObjectRequestHandler handleRequest:inContext:session:application:] () from /usr/lib/libNGObjWeb.so.4.9
0000034 0x00007ffff6c8e85e in -[WORequestHandler handleRequest:] (self=0x555555b48d50, _cmd=<optimized out>, _request=0x55555614c340) at WORequestHandler.m:237
0000035 0x00007ffff6c5633c in -[WOCoreApplication dispatchRequest:usingHandler:] (self=0x5555558b7ac0, _cmd=<optimized out>, _request=0x55555614c340,
handler=0x555555b48d50) at WOCoreApplication.m:712
0000036 0x000055555555c99e in -[SOGo dispatchRequest:] (self=0x5555558b7ac0, _cmd=<optimized out>, _request=0x55555614c340) at SOGo.m:565
0000037 0x00007ffff6ce99fd in -[WOHttpTransaction _run] (self=0x555555ea28a0, _cmd=<optimized out>) at WOHttpTransaction.m:596
0000038 0x00007ffff6ceaec8 in -[WOHttpTransaction run] (self=0x555555ea28a0, _cmd=<optimized out>) at WOHttpTransaction.m:649
0000039 0x00007ffff6ce5f5a in -[WOHttpAdaptor runConnection:] (self=0x555555c242b0, _cmd=<optimized out>, _socket=<optimized out>) at WOHttpAdaptor.m:367
0000040 0x00007ffff6ce6da6 in -[WOHttpAdaptor _handleAcceptedConnection:] (self=0x555555c242b0, _cmd=<optimized out>, _connection=0x5555561686e0)
at WOHttpAdaptor.m:401
---Type <return> to continue, or q <return> to quit---
0000041 0x00007ffff6ce713a in -[WOHttpAdaptor _handleConnection:] (self=0x555555c242b0, _cmd=<optimized out>, connection=0x5555561686e0) at WOHttpAdaptor.m:460
0000042 0x00007ffff6ce71c4 in -[WOHttpAdaptor acceptConnection:] (self=0x555555c242b0, _cmd=<optimized out>, _notification=<optimized out>)
at WOHttpAdaptor.m:521
0000043 0x00007ffff5456d07 in -[NSNotificationCenter _postAndRelease:] (self=0x555555898e00, _cmd=<optimized out>, notification=0x555556020350)
at NSNotificationCenter.m:1307
0000044 0x00007ffff5561b3b in -[GSRunLoopCtxt pollUntil:within:] (self=<optimized out>, _cmd=0x7ffff5946900 <_OBJC_SELECTOR_TABLE+1216>,
milliseconds=<optimized out>, contexts=<optimized out>) at GSRunLoopCtxt.m:642
0000045 0x00007ffff549f840 in -[NSRunLoop acceptInputForMode:beforeDate:] (self=0x555555b8f220, _cmd=0x7ffff58fcfc0 <_OBJC_SELECTOR_TABLE+384>,
mode=0x7ffff5947770 <_OBJC_INSTANCE_2>, limit_date=0x555555b375c0) at NSRunLoop.m:1217
0000046 0x00007ffff549fcf2 in -[NSRunLoop runMode:beforeDate:] (self=0x555555b8f220, _cmd=0x555555b39930, mode=0x7ffff5947770 <_OBJC_INSTANCE_2>,
date=0x555555abcca0) at NSRunLoop.m:1288
0000047 0x00007ffff6c5771e in -[WOCoreApplication run] (self=0x5555558b7ac0, _cmd=<optimized out>) at WOCoreApplication.m:584
0000048 0x000055555555c2bf in -[SOGo run] (self=0x5555558b7ac0, _cmd=<optimized out>) at SOGo.m:326
0000049 0x00007ffff6c7bf54 in WOApplicationMain (_appClassName=_appClassName@entry=0x555555761600 <_OBJC_INSTANCE_0>, argc=argc@entry=13,
argv=argv@entry=0x7fffffffec58) at WOApplicationMain.m:42
0000050 0x00007ffff6c97c8f in WOWatchDogApplicationMain (appName=0x555555761600 <_OBJC_INSTANCE_0>, argc=13, argv=0x7fffffffec58)
at WOWatchDogApplicationMain.m:1043
0000051 0x000055555555a7ab in main (argc=13, argv=0x7fffffffec58, env=<optimized out>) at sogod.m:51

What is the URL of the web calendar?

The error occurs when you click on the calendar

https://test.sample.de/SOGo/so/test.user@sample.de/Calendar/view

But I've anonymised the domain and the email address.

That's NOT a ICS-based URL from SOGo. Ask for the calendar properties to know the real URL to use.

Or do you mean the user is simply trying to enable/disable the calendar from the SOGo web interface?

The use of "web calendar" can be confusing, since web calendars in SOGo are ICS subscriptions.

Try to reproduce the issue and in gdb, when the exception occurs, do:

f 6
po folder
po NSStringFromClass([folder class])

Paste the result of the 3 commands here.

The problem is - I cannot access the properties from the user, because of the "Bad gateway" error.
But from a admin account it's shown as:

https://test.sample.de/SOGo/dav/test.user@sample.de/Calendar/personal.ics

And from my browser I can download it.

The user wants to access his calendar in the Browser.

Here's the output of the 3 commands:

Breakpoint 1, -[NSException raise] (self=0x5555566f5340, _cmd=0x7ffff58fcfc0 <_OBJC_SELECTOR_TABLE+384>) at NSException.m:960
960 NSException.m: Datei oder Verzeichnis nicht gefunden.
(gdb) f 6
0000006 0x00007fffe984d6cb in -[UIxCalendarSelector calendars] (self=0x5555560fd020, _cmd=<optimized out>) at UIxCalendarSelector.m:167
167 UIxCalendarSelector.m: Datei oder Verzeichnis nicht gefunden.
(gdb) po folder
svetlana_D_iliaeva_A_sample_D_de_AE6-5755F280-1-4092D880
(gdb) po NSStringFromClass([folder class])
GSMutableString

svetlana_D_iliaeva_A_sample_D_de_AE6-5755F280-1-4092D880 is a shared calendar from an other user.
And this is maybe the deleted calendar.

I cannot reproduce this...

When doing f 6, also do:

po sortedFolders
po folderName

Here's the output:

Breakpoint 1, -[NSException raise] (self=0x5555562974e0, _cmd=0x7ffff58fcfc0 <_OBJC_SELECTOR_TABLE+384>) at NSException.m:960
960 NSException.m: Datei oder Verzeichnis nicht gefunden.
(gdb) f 6
0000006 0x00007fffe984d6cb in -[UIxCalendarSelector calendars] (self=0x55555606c750, _cmd=<optimized out>) at UIxCalendarSelector.m:167
167 UIxCalendarSelector.m: Datei oder Verzeichnis nicht gefunden.
(gdb) po folder
svetlana_D_iliaeva_A_sample_D_de_AE6-5755F280-1-4092D880
(gdb) po sortedFolders
("<0x555556026db0[SOGoAppointmentFolder]: name=personal container=0x5555561450f0/Calendar ocs=/Users/jochen.becker-gruell@sample.de/Calendar/personal>", "<0x55555615b6c0[SOGoAppointmentFolder]: name=enver_D_oezguer_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/enver.oezguer@sample.de/Calendar/personal>", "<0x5555560732b0[SOGoAppointmentFolder]: name=fevzi_D_cebe_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/fevzi.cebe@sample.de/Calendar/personal>", "<0x555555f4c290[SOGoAppointmentFolder]: name=maggie_D_berg_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/maggie.berg@sample.de/Calendar/personal>",
"<0x555556175f90[SOGoAppointmentFolder]: name=pascal_D_marquardt_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/pascal.marquardt@sample.de/Calendar/personal>", "<0x5555561c8350[SOGoAppointmentFolder]: name=sarah_D_ince-kemen_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/sarah.ince-kemen@sample.de/Calendar/personal>", "<0x555556160980[SOGoAppointmentFolder]: name=svetlana_D_iliaeva_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/svetlana.iliaeva@sample.de/Calendar/personal>", "<0x55555617e3d0[SOGoAppointmentFolder]: name=uwe_D_dannert_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/uwe.dannert@sample.de/Calendar/personal>", "<0x555555ea1080[SOGoAppointmentFolder]: name=vera_D_bausch_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/vera.bausch@sample.de/Calendar/personal>", "<0x5555561dd4e0[SOGoAppointmentFolder]: name=volker_D_brenn_A_sample_D_de_personal container=0x5555561450f0/Calendar ocs=/Users/volker.brenn@sample.de/Calendar/personal>", "svetlana_D_iliaeva_A_sample_D_de_AE6-5755F280-1-4092D880", "<0x5555561d2610[SOGoWebAppointmentFolder]: name=6420-57583380-1-75E74100 container=0x5555561450f0/Calendar ocs=/Users/jochen.becker-gruell@sample.de/Calendar/6420-57583380-1-75E74100>", "<0x555556184910[SOGoWebAppointmentFolder]: name=641E-57583400-1-1A80C240 container=0x5555561450f0/Calendar ocs=/Users/jochen.becker-gruell@sample.de/Calendar/641E-57583400-1-1A80C240>", "<0x555556175a40[SOGoWebAppointmentFolder]: name=6420-57583400-3-75E74100 container=0x5555561450f0/Calendar ocs=/Users/jochen.becker-gruell@sample.de/Calendar/6420-57583400-3-75E74100>")
(gdb) po folderName
Cannot access memory at address 0x0
(gdb) po folder
svetlana_D_iliaeva_A_sample_D_de_AE6-5755F280-1-4092D880
(gdb) po NSStringFromClass([folder class])
GSMutableString

Tomorrow I will tell you how I fixed the problem - but I think it's still a bug and should be fixed in the code.

No need, found and fixed the bug.