Plan vanilla 43.2 KDE installs updated to Leap 15 according to SDB Documentation (init 3 and zypper dup after renaming repos, looked fine in the beginning). After some time up and running the systems show signs of degradation, sometimes Dolphin can’t open files (unable to create slaves type file or samba), sometimes the Application Launcher simply does not open any more, sometimes the complete panel disappears with “Could not connect to D-Bus” error.
All 3 machines I updated recently are hardly usable any more. On one machine I did in zypper a reinstall of all installed packages, which completed with an error (I didn’t find any error messages in the output though).
If you use the same “/home/USER”-directories which you used with openSUSE Leap 42.3 then the problems may be caused by incompatible configurations (e.g. in /home/USER/.config).
Things worth trying:
Create a new user (with an empty “/home/NEWUSER”) and see wether that user performs “normal”. If so you can move old config files one by one to the new directory in order to see what is causing the problem.
Delete all files in “/tmp” and “/var/tmp”. Make sure that there are no running services which access those directories. (Ideally use the rescue-environment from the openSUSE Leap installation media)