Folks, following a suggestion from Michel Dänzer, one of mutter’s lead devs, I replaced mesa-freeworld packages for their vanilla counterparts, removed the udev rule, and didn’t experience the problem. It seems this odd behavior is a side-effect from using these packages.
(@py0xc3 you raised concerns about mesa-freeworld before everyone else 
)
So, AFAICS there are two possible solutions:
- Don’t use mesa-freeworld from RPMFusion
- Use mesa-freeworld with the special udev rule
I’ll mark this as the solution for future reference, file a bug report on RPMFusion, and update the other bug reports accordingly. Thanks to all who contributed, it’s always nice to see this collective mind working 
Fedora community is awesome 