Did you clear your browser cache?

Yes, of course. I tried with Chrome, Firefox and with an Android Tablet... :-(

Show the complete list of SOGo/SOPE/GNUstep packages installed.

Meanwhile, many thanks, because I do not know exactly where to start ...

dpkg --get-selections |grep "sogo"
sogo:amd64 install
sogo-activesync install

dpkg --get-selections |grep "sope"
libsope-appserver4.9 install
libsope-core4.9 install
libsope-gdl1-4.9 install
libsope-ldap4.9 install
libsope-mime4.9 install
libsope-xml4.9 install
sope4.9-gdl1-mysql install
sope4.9-libxmlsaxdriver install

dpkg --get-selections |grep "gnustep"
gnustep-base-common install
gnustep-base-runtime install
gnustep-common install
gnustep-make install
libgnustep-base1.24 install

Better install apt-show-versions and get the versions from that.

apt-show-versions |egrep 'sogo|sope|gnustep'

Nice trick. I did not know it. Thank you.

apt-show-versions |egrep 'sogo|sope|gnustep'
gnustep-base-common:all/jessie 1.24.7-1 uptodate
gnustep-base-runtime:amd64/jessie 1.24.7-1 uptodate
gnustep-common:amd64/jessie 2.6.6-3 uptodate
gnustep-make:all/jessie 2.6.6-3 uptodate
libgnustep-base1.24:amd64/jessie 1.24.7-1 uptodate
libsope-appserver4.9:amd64/jessie 4.9.r1664.20170721 uptodate
libsope-core4.9:amd64/jessie 4.9.r1664.20170721 uptodate
libsope-gdl1-4.9:amd64/jessie 4.9.r1664.20170721 uptodate
libsope-ldap4.9:amd64/jessie 4.9.r1664.20170721 uptodate
libsope-mime4.9:amd64/jessie 4.9.r1664.20170721 uptodate
libsope-xml4.9:amd64/jessie 4.9.r1664.20170721 uptodate
sogo:amd64/jessie 3.2.10.20170817-1 uptodate
sogo-activesync:amd64/jessie 3.2.10.20170817-1 uptodate
sope4.9-gdl1-mysql:amd64/jessie 4.9.r1664.20170721 uptodate
sope4.9-libxmlsaxdriver:amd64/jessie 4.9.r1664.20170721 uptodate

As you use a nightly build, could you upgrade to the current one?

I use the nightly build version because I do not have an Inverse subscription for the moment. Sorry. :-(

Try disabling PageSpeed.

You are my hero! Yes, disabling pagespeed in nginx.conf (pagespeed off;) solved the problem. I was thinking about a some cache problem, but I did not exactly remember about pagespeed. Thank you very much!
Ad majora!

Hi,
I have the same problem with a nightly uptodate with Nginx in front web but without pagespeed module.
The source code is available but nothing is randering.

At the begin of source code there is two empty line.

ii sogo:amd64 3.2.10.20170828-1 amd64
ii sogo-activesync 3.2.10.20170828-1 amd64

ii libsope-appserver4.9 4.9.r1664.20170721 amd64
ii libsope-core4.9 4.9.r1664.20170721 amd64
ii libsope-gdl1-4.9 4.9.r1664.20170721 amd64
ii libsope-ldap4.9 4.9.r1664.20170721 amd64
ii libsope-mime4.9 4.9.r1664.20170721 amd64
ii libsope-xml4.9 4.9.r1664.20170721 amd64
ii sope4.9-gdl1-mysql 4.9.r1664.20170721 amd64
ii sope4.9-libxmlsaxdriver 4.9.r1664.20170721 amd64

ii gnustep-base-common 1.24.7-1 all
ii gnustep-base-runtime 1.24.7-1 amd64
ii gnustep-common 2.6.6-3 amd64
ii gnustep-make 2.6.6-3 all
ii libgnustep-base1.22 1.22.1-4+deb7u1 amd64
ii libgnustep-base1.24 1.24.7-1 amd64

Why is libgnustep-base1.22 installed?

The server who bug appear is an old Debian 7 who upgrades to Debian 8, it's probably the cause. We pass regulary apt-get autoremove to remove old unused packages but 1.22 it's not listed to be removed.

I have remove the 1.22 package and restart Sogo without change.