The Unexpected Error Handler warning is issued in the following situations:
'Abort Transaction' should be set to 'Yes' for 'AllException' error handler at screen flow level: you have an Error Handler, in a screen flow, to catch general exceptions and the Abort Transaction property is set to No.
You should change the Abort Transaction property to Yes because, since the Error Handler is catching all exceptions, the current database transactions should be aborted to avoid having inconsistent data committed.
Clicking the symbol will take you directly to the Error Handler element in your flow.
Handle Exceptions | About Warning Messages