Ran the backups again last night, still stopping after 1 hr of running, starts up 2hr later and repeats pattern afterwards.
Settings for last nights autobackups:
Server scheduled task for autobackups default value of every 50th minute
Course backups 8pm
Results:
850pm-950pm courses backed up
1150pm-1250 courses backed up
250am-350am courses backed up
550am-650am courses backed up
190 couorses total, which grows after each run by about 45, still about 450 left to do.
Clear pattern of 1hr of backing up, followed by 2 hrs of no backing up, then starting up again.
The backups stop and start on the 50th minute so it looks like the server scheduled task for autobackups is the culprit stopping the backups. I will consider running the server scheduled task for autobackups every 8 hr next.