I've attached a strace of software-properties-gtk, taken with the "strace -fr -o software-properties-gtk.strace software-properties-gtk" command. The only thing which stands out to me is that there are a *lot* of EAGAIN entries for file descriptor 3, which appears to be the local "/tmp/.X11-unix/X0" socket. The file exists, and has what I'd expect to be usable ownership and permissions.
$ ls -l /tmp/.X11-unix/X0 srwxrwxrwx 1 adric adric 0 Feb 12 09:24 /tmp/.X11-unix/X0 AS PJSingh5000 indicated, the only message displayed on the terminal was ERROR:root:Authentication canceled, changes have not been saved ** Attachment added: "strace of software-properties-gtk" https://bugs.launchpad.net/ubuntu/+source/software-properties/+bug/1660100/+attachment/4817552/+files/software-properties-gtk.strace -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1660100 Title: Unable to enable or disable repository in Software & Updates To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/software-properties/+bug/1660100/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs