Error when sending batch request for ViewCalendar: invalid character '<' looking for beginning of value

[mickmister]

And another one:

(log ERROR) Error during user status sync job. err=not able to get calendar views for connected users: msgraph ViewCalendar batch request: invalid character '<' looking for beginning of value

Issue created from a Mattermost message by @jprusch.

[Kshitij-Katiyar]

@wiggin77 @jprusch
I spent considerable time attempting to reproduce the issue but was unable to do so. Upon further investigation, the only plausible explanation I found is that the MSGraph bulk request API might return an HTML response in certain scenarios, leading to this error. However, I was unable to pinpoint the exact circumstances.
If you are still encountering this issue, please let us know. Additionally, if you could provide detailed steps to reproduce the problem, it would be greatly appreciated.