Connector is returning 401 when actual error is "The remote server returned an error: ("503") Server Unavailable.
When SharePoint returns: "The remote server returned an error: (503) Server Unavailable" to the connector, the connector should return 503. Right now it's returning 401. 401 causes Logic App to not retry, where 503 would. This happens a lot when MS are doing feature updates. If Logic App retry policy kicked in, it may have gone through just fine.