I've upgraded UIM/UMP 9.2.0 to UIM/OC 20.3 and all seems OK but I can't log in to OC with any contact/account user but I can login with the administrator.
The Accounts created in UMP 9.20 are present in the Database but I can't log in with any of them.
I have also noticed that I cannot create new ACLs in the Account Admin app in the Operator Console.
The cause of this issue is most likely a corrupt security.cfg.
To restore the security.cfg from an existing backup use the following KB Article/Guide:
UIM - Use the secedit utility to recover or modify the security.cfg