[tor-relays] Exit stops after one year, then again after few days

[ylms]

Hello all
As written above, I run an Exit (for many years, with the current setup
since 04.2019) but on 30. March 2020 it stopped, I was unable to
determine any reason.
So I installed updates and since there were some Kernel updates I also
rebooted the machine. The Exit was back up and ran again till ~36h ago.
Same situation again, I have no idea why it stopped.

I now activated "Log notice syslog", I think this was in the standard
torrc which is installed with the package of Ubuntu 18.04.4 LTS anyway,
but there is not entries in journalctl. Only Start/Stop/Reload events
are shown in the journal for unit tor.service since 100 day ago.

Can someone help me to troubleshoot this problem, could the fingerprint
be blacklisted? In this case would the Exit come back up running for a
few days as described above?

Regards and thank you very much for any support.
yl