Calendar issue

[JP Horst]

After upgrade to 3.1 on Centos we have problems with the calendar in roundcube 
(Users usually use kontact in parallel). We use a joint view for 9 users.

Starting the initial view usually but not always shows all appointments 
correctly.
However loading the view takes unreasonably long (e.g. 35 seconds). After the 
loading an update cycle starts, which usually ends in an "Internal Server 
Error" message (sometimes also Server Timeouts).
If we leave the browser then untouched for a while, appointments vanish from 
the view. Actively choosing the same week again, shows all appointments again 
(after lengthy loading).

The roundcube logs mysl and imap grew to 2-3 GB within 7h. The content of the 
logs do not look like error messages.

The https/error_log shows loads of entries like:
unnamed app(2780) KolabV2::Incidence::loadAttribute: Saving unhandled tag 
"revision"
unnamed app(30609) KolabV2::Incidence::loadAttribute: Saving unhandled tag 
"revision"
unnamed app(2783) KolabV2::Incidence::loadAttribute: Saving unhandled tag 
"revision"

Any help with this, where to look for clues and how to solve this, is greatly 
appreciated.

Kind regards,
Jens

PS: Chwala also produces an error, if a file is already uploaded and if a 
second file shall be uploaded. This is however not very critical for us. I do 
not know if this can be connected somehow.