Hello Teams!
An Azure customer @larsklint via Twitter is experiencing an Active Directory user login issue and can only add the user with a workaround. Logging in the user only works when it is not "required" despite that the user is assigned to the application. The only way to get it to work is to make the user the application owner.
The customer confirmed that they steps listed in this document: https://aka.ms/d1164606
Thank you!