FYI, I've now read of a couple of people having issues with the Viltrox adapter.
I don't think these adapters have any additional chips or programming, just straight-through contacts. When heavy L lenses are mounted, they are probably having mechanical contact issues, as I can feel a slight "give" at the camera side. however, my Canon-brand 2x III TC also has similar amount of "give," so if "clean contact" warning comes up, one could probably just unmount and remount the adapter. I paid $45, so I can't complain..