I suspect this is related to the group sharing issue first reported here:
https://community.esri.com/t5/arcgis-enterprise-portal-questions/portal-for-arcgis-11-1-can-no-longe...
but I am no longer able to 'change owner' of portal users' items from user to user, where those users role privileges would normally allow them to own items - e.g. changing owner from one publisher to another.
I have to make the user that I want to take ownership an Administrator, then I can change ownership. I then have to go back and change the user role back to Publisher (or custom role)
