ATP UI is showing an error "SEPM connection token refresh failed; verify SEPM login credentials". When you add the SEPM credentials back after a few hours it fails again.
SEPM connection token refresh failed; verify SEPM login credentials
If you have more then one Symantec Endpoint Protection Manager (SEPM) manager that logs into the same SQL server for the database, the recommendation is to create a separate account on SEPM to have ATP connect to SEPM using this exclusive account for ATP.