This feels like a very stupid problem, and hopefully I'm simply overlooking something.
I regularly make updates to a ArcGIS Pro project and overwrite an existing service in our enterprise GIS (We are utilizing Portal, ArcGIS Server, DataStore, Federated Servers etc).
Under normal circumstances when I "re-publish" a service from ArcGIS Pro using Share As > Web Layer it overwrites the Service Layer in Portal and the the Map Service on ArcGIS Server. This has never been a problem in the past.
In my most recent update, when I published the service it failed and gave me no error messages of any kind other than a very generic message that it could not publish the service.
If i try to publish a new service with a new name it publishes fine.
If i delete the service from Portal and ArcGIS Server and try using the same name as I previously used. It fails.
What am I missing here? Are there locks on the service or some sort of legacy file that isn't being deleted when I delete the service? I've tried restarting ArcGIS Server and looking at the logs for clues (which aren't much help).