After updating just the packages on our control panel server to prepare for v11 upgrade I got this spamming journalctl
systemd[5786]: srs_milter.service: Failed to determine user credentials: No such process
systemd[5786]: srs_milter.service: Failed at step USER spawning /usr/sbin/srs_milter: No such process
systemd[1]: srs_milter.service: Main process exited, code=exited, status=217/USER
systemd[1]: srs_milter.service: Failed with result 'exit-code'.
systemd[1]: srs_milter.service: Scheduled restart job, restart counter is at 54.
systemd[1]: Stopped Enhance SRS milter.
I have raised a support ticket