Azure AD driver 5.1.7.300 error publish: AADSTS50034: The user account {EUII Hidden} does not exist in the xyz.onmicrosoft.com directory

I have just installed the Azure AD driver 5.1.7.300 patch updating an existing 5.1.7.200 configuration in a test environment.

After starting the driver it was shut down again with the following error message:

publish: AADSTS50034: The user account {EUII Hidden} does not exist in the xyz.onmicrosoft.com directory. To sign into this application, the account must be added to the directory. 

I couldn't find any further info on the origins of this user, I certainly don't have an EUII Hidden account and the user previously configured in the driver still exists.

I can't find others mentioning this so far, so I wonder if anyone else has encountered this?