Re: Panic: file mail-user.c: line 185 (mail_user_deinit): assertion failed: ((*user)->refcount == 1)

Try to cd to the maildir main directory e.g. cd /home/szots/mail and run
the force-resync command from there. It might work.

Unfortunately, it didn't work. However, when I commented out FTS, it allowed the resync to finish:

mail_plugins { # fts = yes # fts_flatcurve = yes }

It's seems it's something around full-text search implementation.

Even in disabled FTS state, force-resync brings back fts-flatcurve mailboxes. I remove them with "doveadm mailbox delete", then a new force-resync, and they're back there.

Ákos