Azure AD Connect AutoUpgrade Failure

A client of ours has AADConnect 1.1.281.0 installed and working just fine, but every so often we'll find the Microsoft Azure AD Sync service stopped.

Investigating the event logs shows a number of Event ID 303 warnings that point to the AutoUpgrade process (https://docs.microsoft.com/en-us/azure/active-directory/active-directory-aadconnect-feature-automatic-upgrade) failing with the specific details of:

Azure AD Connect AutoUpgrade result = UpgradeAbortedServiceCanNotBeStopped

or

Azure AD Connect AutoUpgrade result = UpgradeAbortedAdSyncExeInUse

Note that it's one or the other, events with these two warning don't log at the same time. I've disabled the AutoUpgrade feature for now, but am curious if anyone else has run into this and how to fix it?

I am going to parse AV logs to see if it's blocking the upgrade/install process, but can't find many other clues. No proxy in use and no firewall rules blocking URLs.

Thanks