sieve not working after migration to 16.1

[Reitelbach, Thomas]

Hi guys,

a few days ago I migrated my kolab server from 3.3 to 16.1.
1) I installed a vanilla kolab 16.1 on a fresh server with centos 7
2) copied over the complete mail spool
3) copied over /var/lib/imap/mailboxes.db / annotations.db
    copied over /var/lib/imap/domain/
    copied over /var/lib/imap/sieve/
4) copied over and imported the LDAP database
5) copied over and imported the SQL Database and applied some 
manipluations on the database (changes in the schema between 3.3 -> 3.4)

So far, so good. It seemed everything was working fine, my users could 
login, send mail, had their calendars and so on. One user lost some 
settings in roundcube, others where fine (no idea why?!).
But now I realize that the sieve scripts are not working. They have been 
copied over, roundcube shows them, but they simply get not applied as 
far as I can tell.
For my own account I tried to remove them via roundcube and set them up 
from scratch, but same behaviour -> simply no filtering happens.
Then I tried the vacation rule. It does use sieve as well, right? 
Vacation is working as expected. What is happening here?

Sorry, I have no idea where to look for the reason and where to activate 
debugging-logs?!
Can someone point me to the right direction for debugging?

Thank you very much
Thomas