Update Kolab16 on Debian 10 - mailboxes still disappear

I know I sound like a broken record...

but my server still is waiting for updates. I tried again. I was able to
use the .deb file which allowed me to finish the upgrade

still, post installation, no errors, my mailboxes are gone


- kolab lm shows none
- logging in via imap to guam shows no mailboxes for my user
- logging in via imap to cyrus shows no mailboxes for my user
[this is not identical to the last time I lost my mailboxes]
- reconstuct shows a seemingly complete list of the users folders

- I am HIGHLY confident that the filesystem is okay and has free space
and all that...

I request your help. I will gladly install the update again and try out
stuff and post logs.
for now, I restored the snapshot