ArcGIS Online: A vague error message "Unable to change owner on item" is returned when an item's owner cannot be changed due to group sharing issues.

Workaround

View the error for the "Reassign" request in the web traffic to identify groups that the new owner is not currently a member of. The new item owner must be a member of all groups the items are currently shared with for the sharing process to succeed.

Steps to Reproduce