When testing access to the Primary or Replica when the appliance is running in Test Mode the users are unable to log in using AD credentials.
They are able to log in using Paradmin/Parmaster (Local) credentials.
This is expected behaviour, external authentication is disabled when the server mode is running in Test Mode.
The appliances would have to be running in Primary mode to access the interfaces using AD credentials.
This is detailed in the TPAMConfigurationAdminManual.pdf page 88.