Comment # 12 on bug 1200140 from Fabian Vogt

(In reply to Episteme PROMENEUR from comment #10)
> Created attachment 859389 [details]
> journal
> 
> Journal after a failed locking.

The cause is:

ksmserver[15810]: /usr/lib/kscreenlocker_greet: symbol lookup error:
/usr/lib64/libKF5WaylandClient.so.5: undefined symbol: wl_proxy_marshal_flags

Which means that you have libwayland-client0 from Leap 15.3 and not the
KDE:Frameworks5 repository. You have to switch over and mark K:F5 as a higher
prio repo (e.g. 98).