A subscription has been created wrongly after trying to import it from another system. The site works fine but the ownership is bugfixsaserv and when trying to change the ownership that is indicated on the subscription (and exists in /etc/passwd) it will not allow me.

I can change owner to rootsaserv but not to any other user setup via Plesk on the interface for the subscription.

It looks to me is preventing also changing the SSL configuration, as I can override nginx.conf for others but not this one.

11.5.30 Update #51
CloudLinux Server 6.5

Any ideas ?

It does not really matter. I tried as root, which means if the user is listed on passwd (that is, the user exists) I should be able to change it.

I can change from bugfix to root, but not to the user I setup on the subscription sadly... it is very odd, I would say it is a kernel thing but obviously Plesk has something to do with it.