I ran out of space on my server so made changes to the amount of full backups to keep etc. The webinterface stopped working and noticed urbackup_srv had vanished from htop 
syslog:
Oct 8 18:21:49 offsitebackup kernel: [2618286.754446] urbackup_srv[25862]: segfault at 0 ip 00007f4912b15e2a sp 00007f4907ff4110 error 4 in liburbackupserver.so.0.0.0[7f4912a9e000+203000]
Oct 8 18:45:09 offsitebackup kernel: imklog 5.8.11, log source = /proc/kmsg started.
Oct 8 18:45:09 offsitebackup rsyslogd: [origin software=“rsyslogd” swVersion=“5.8.11” x-pid=“5845” x-info=“http://www.rsyslog.com”] start
Oct 8 18:45:09 offsitebackup rsyslogd: [origin software=“rsyslogd” swVersion=“5.8.11” x-pid=“5845” x-info=“http://www.rsyslog.com”] rsyslogd was HUPed
There’s nothing indicative in the urbackup.log