Ok - I stopped HBS3, and the failed logins are still happening.
On the 28th:
1 at 13:35
7 between 16:30 and 16:34
On the 29th:
1 at 15:54
1 at 16:41
1 at 17:32
It’s also worth noting that when HBS3 was enabled, the various sync and backup jobs I have configured were all working just fine.