I’m glad I found this post. I’ve been having the same problem on an RPI4 for a few months now, but I haven’t had time to investigate it further. So I can’t say if the fix works or not. BTW: At first I thought it had something to do with Wayland. But it doesn’t look like it. I will report if and what fixed my problem.
Edit:
Masking “dev-dri-card0.device” and “dev-dri-renderD128.device” solved my problem! I use XFCE with lightdm by the way and don’t have the option “dtoverlay=vc4-kms-v3d” in “/boot/config.txt”. The Problem came with an update but i can not remember when. Affected is a Pi4 and a Pi400.