To us, the problem with kscreenlocker crashing seems solved or circumvented. It did not happen again since we changed NIS and name server configuration like reported in my last comment. (And we were installing two new machines with openSUSE Leap 15.1 per week since some months.) Nevertheless, I am still wondering: If it was a problem with NIS configuration, why did it only affect the kscreenlocker program and nothing else? And if it was caused by our system configuration, why did it only affect a few users? We manage all users in NIS and all accounts are set up the same way. If you like to further examine this or do some more troubleshooting, I would be happy to support you. I also currently do have a workstation dedicated to experiments like this.