All email accounts are showing no emails available and they seem to vanish after a period of time on the server when/if they do manage to come in...
I had the same issue after the recent update. I think rebuilding mail server resolved the problem for me.
Same issue for me.
The email are not coming in. The Dovecot IMAP/POP3 Server is not running.
[edit]
I found the solution:
In the log file I see the error.
There was an error in /etc/dovecot/sni.conf file.