When updating the packages, sometimes Discover shows in its output: PackageKit stopped running! and the "Checking for updates..." (Looking for updates) messages are kept on discover forever, as if the connection with packagekitd was lost. After some debugging, it seems packagekitd can be configured to end automatically after some idle time (Just set ShutdownTimeout=15 under [Daemon] in /etc/PackageKit/PackageKit.conf), and that confuses Discover. Note that openSUSE did install a default of ShutdownTimeout=15 in the past, so old systems may have that config option. This was done because of a bug in libzypp (https://bugzilla.opensuse.org/show_bug.cgi?id=899755) which was fixed in 2017. Since last August, the option is no longer used in new installations, but old ones still use it.
Enabled the packagekitd timeout and didn't break. However your symptoms look alot like this other issue. I'm submitting a fix for it, should be on the next stable release. *** This bug has been marked as a duplicate of bug 389072 ***