Automatic backups are a hit or miss

Is there anything specific that I should be looking for?
I was searching the logs for last few days with “backup” as the search keyword and Production.log only had entries for the manual backups I triggered or the times when I visited backup page:
e.g.
Started GET "/admin/backups/status.json?_=1529382308307" for xxx.xxx.xx.xxx at 2018-06-19 05:31:30 +0000
I don’t think that tells much about the situation.

in the logs web UI, there are a lot of these:
TypeError: Discourse._registerPluginCode is not a function at https://discourse.orng.co/u/activate-account/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx:46:21
but those are from a 11th June (backup ran successfully on 14th though!