Seems there is really a problem : I can see new functionnalities (project list for example), the some things are broken (can't create new project, function sortXXXXXXX is missing).

Rolling back.

Is there a good way to troubleshoot this king of issue ?

After overwriting old code with new code, disconnect and reconnect as Admin : this should finish with DB upgrades.
In your case it seems DB upgrades failed : have a llok at log files to understand issues, fix and try again.

Ok, so the upgrade went wrong...

I can see some errors in the log:

** ERROR ** [V12.1.2] Error on SqlElement to get 'mustChangePassword' for Class 'User' : field 'mustChangePassword' not found in Database.

** ERROR ** [V12.1.2] [4] Error on SqlElement to get 'defaultDuration' for Class 'ActivityType' : field 'defaultDuration' not found in Database.

Grepping these values in projeqtor/db/ it seems these fields are created in the 12.2.0 script. But I tried to install 12.2.1 directly from 12.1.2. That might be the problem ?

Ok, starting fresh, step by step, release by release.

Right now I'm at v12.1.2.
In projeqtor/db, latest script is projeqtor_V12.1.2.sql
In projeqtor/db/, all files are dated 7 May.

So I :
1) disconnect every user
2) close the application
3) logout
4) unzip -uo projeqtorV12.1.3.zip into /var/www
5) recursively chown the directory to www-data
6) restart apache
7) log into projeqtor as admin
But... nothing seems to happen. Shown version is still 12.1.2. No database update message is shown.

Log says: ----- DEBUG ----- loginCheck : current db version = 'V12.1.2'
and let me log in happily.
In projeqtor/db, latest script is now projeqtor_V12.1.3.sql and files are dated 17 June.
But the tentative upgrade seems unnoticed...

What is the way Projeqtor can tell an upgrade is ongoing ? I might have a "marker" file lyong around or something... ?

Ok, answering my own question: it seems projeqtor compares dthe version stored in database with $version in tool/projeqtor.php.

It seems my 'unzip -uo ' command was not overriding some file, including tool/projeqtor.php, hence the upgrade unnoticed.
So I did 'unzip -o ' and that time all went smoothly...

Final thought: it's probably time to subscribe to the auto-update service, as Projeqtor is really a very very valuable piece of software, and supporting the company behind it is the least we can do...

Thanks a lot to the team !