To clarify - what are you trying to do on the domain? Are you just logging into the Azure portal or trying to access certain resources?
Are the users logging in with User Principal Name or primary email address? Make sure that you are logging in with User Principal Name.
Also, are you using Pass-Through? If so, the pass-through agent should be installed on the domain controller.
Not to state the obvious, but you can also try a fresh password reset, make sure "change password upon next logon" is not ticked, and clear the cache and try again from a new browser and incognito window.