I’m using Full Wayland KDE and when I lock the screen, the screenlocker/saver dies immediately when I shut off my TV with an error that says to use loginctl unlock-sessions to unlock the broken screenlocker/saver BUT IT DOESN"T WORK. The only thing that works is a reboot. I opened a KDE Bug and about 7 others so far said they have the same problem and one of them noticed that we all use AMD Radeon GPUs. The Bug number is 439096
I think this information will benefit lots of KDE users. Thank you for being so kind to share it. 
The bug has been fixed. Needs to be verified. Expected to be in the 5.23 version of KDE Plasma.