That must be different problems. Mamiya 24 FE, 35, 50 Shift, 80, 200 APO etc ... reach with the Fotodiox Pro Adapter M645-GFX all perfectly infinite on the GFX.
If the Mamiya 105-210 does it only at the 140mm, I'll tap on another problem.
However, I noticed a very fluctuating quality in my Fotodiox adapters. Maybe that's one reason.
The best mechanical adapters with the lowest tolerances had Kipon until now.
Greeting Gerd
addendum:
My Mamiya lenses are all about infinity. That's right, because the material of the lenses expands at different temperatures.
In this respect, that must already be a very strong deviation on the adapter.