Hi everyone
I just wanted to add some further information on this message
I recently experienced the same message "the service is owned by another user. The sharing properties can only be shared by the owner" but within ArcGIS Server Manager's sharing properties.
I have a High Availability, active\active environment in 10.7.1 - 1 portal site with a primary and standby machine. The Portal site is federated to ArcGIS GIS Server site with two machines
We found that this error was introduced each time I renamed one or both AGS machines from fully qualified domain name to dns name. Enterprise is designed to communicate within itself using fully qualified domain names so anything different, such as a dns machine name) throws a 401 error in the web browser when ArcGIS Server machine is trying to access Portal site.
Thanks Ed