Youtrack backups not reliably generated

Hi all,

I'm running a standalone instance of Youtrack 2018.3 Build 46358, and can't seem to get scheduled backups working reliably. I've chosen "Every day at 2am" as the backup schedule, but on most days then no backup is generated. Even on the days when it is, then it appears at an unpredictable time during the day, e.g. on the 20th November there's a backup timestamped 06:13, with the previous backup 15 days ago.

Manually running a database backup seems to work reliably every time though.

Looking through the logs, I can see ocassional entries stating "Start BackupDatabaseScheduling", "Starting 'BackupDatabaseScheduling' with '0 0 2 * * ?'." and "BackupDatabaseScheduling started"; it looks like these correspond to the times I've started Youtrack rather than the actual backup job running though.

One thing that does look odd to me in the logs is frequent entries indicating a large number of pending QuartzJobProcessor jobs (e.g. "There are 47900 pending jobs in QuartzJobProcessor") - the number of jobs seems to keep increasing and never drops. The statistics page doesn't seem to show anything out of the ordinary though (see below).

Any ideas as to what might be going on here, or what else I could do to debug this? Youtrack and the virtual machine I'm hosting it on seem to be otherwise working fine.