After changing the Application Identity to a new account and password, the Notification Server, some other Task Servers, and many clients were not able to register to a Task Server.
Error type: HTTP error
Error code: HTTP status 401: The request requires user authentication (0x8FA10191)
Error note: Authentication failed, server refused to authenticate with the provided credentials or the user account is locked
The Agent Connectivity Credential in the Notification Server communications profile was configured to use the old Application Identity account and password.
Disabled the override of the Global Agent Settings policy > Authentication tab.