I think alot of the better shooters are shooting paper. Especially 1" dot drills and things like the SH and MDS sniper drill. They are great practice and you are right, paper doesn't lie. They would be reporting it. I know chad and francis zero after every day
The question is, if there was a shift why wouldn't it persist? If you zero at beginning of match and at end of each day, and see no change, or across days, then how is it explained? A tenth is within the noise elevation wise with most shots.
The only thing that makes sense IMO, is people abusing their equipment. I know exactly what they mean by letting it fall, say from position 3 to 4 on the PRS barricade. Its about 20" by spec. I can't recall anyone letting the weight of the gun just drop on a hard sand bag rested on a steel rail. You can do a controlled decent with the grip but most people, actually grab their bag and the gun with the support hand, especially if they are running a plate or attached bag.
IMO its no different than any of the above mentioned examples where we know you will get POI shift from banging your gun/optic around.