“The operation completed successfully”???? What the?????
The Event ID: 7001 might give us a clue. But after having a google around, it does not. My guess* is that one of the Exchange System Attendant services (perhaps MTA Stacks?) has a bigger issue, which needs to be looked into further.
* Dale has worked as the mail administrator for a 100-site email system. It wasn’t as reliable as Exchange.