We have the same problems with shared calendars. Workaround is to save the appointment and then edit it again -> voilà, calendar selection is possible

Converting a mail to an appointment or task is broken, too: its not possible to select any calendar at all.

the commit https://github.com/Alinto/sogo/commit/3eeebbc83be064e65138ee6f777e1eaf0e2b5931 doesn't fix the issue: as its a javascript change, is just a "update generated files" commit like in https://github.com/Alinto/sogo/commit/82747746c6617b49889adf7d85e482226f41ed3c missing?

if so, why isn't this part of the build / compile step?

@abma : the is already the case. Something was broken during server migration.

The following procedure can fix the issue :

service sogo stop
mv /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Common.js 
/usr/local/lib/GNUstep/SOGo/WebServerResources/js/Common.js.bak
mv /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Common.js.map 
/usr/local/lib/GNUstep/SOGo/WebServerResources/js/Common.js.map.bak
mv /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Scheduler.services.js 
/usr/local/lib/GNUstep/SOGo/WebServerResources/js/Scheduler.services.js.bak
mv /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Scheduler.services.js.map 
/usr/local/lib/GNUstep/SOGo/WebServerResources/js/Scheduler.services.js.map.bak
wget 
https://raw.githubusercontent.com/Alinto/sogo/master/UI/WebServerResources/js/Common.js
 -O /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Common.js
wget 
https://raw.githubusercontent.com/Alinto/sogo/master/UI/WebServerResources/js/Common.js.map
 -O /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Common.js.map
wget 
https://raw.githubusercontent.com/Alinto/sogo/master/UI/WebServerResources/js/Scheduler.services.js
 -O /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Scheduler.services.js
wget 
https://raw.githubusercontent.com/Alinto/sogo/master/UI/WebServerResources/js/Scheduler.services.js.map
 -O /usr/local/lib/GNUstep/SOGo/WebServerResources/js/Scheduler.services.js.map
service sogo start

When the release will be out, do not forget to delete .bak
files.
You also need to clear your browser cache.