I'm speaking only from my personal experience, but I have witnessed it multiple times when I have doubled up on deer...and I know folks that I hunt with who have had similar experiences, even at close range. One hunt in particular that stands out in my mind was when I was less than 20 yards from two does standing, one in front of the other just a few feet apart. I shot one (unsuppressed .270 Win.) and she dropped. The other doe just stood there while I chambered another round. So, she did not even react to the sound of me working the bolt. I shot her while she was still standing there. This was in an area that had a lot of hunting pressure.
Mine is definitely a small sample size compared to yours, but it has happened "often" enough that I'm not really surprised when it does happen or when I hear reports of similar experiences from other hunters that I know. I have no explanation for it. I would think that shooting a .270 that close to a deer would scare the hell out of it.
I have no doubt that suppressed shots spook deer less frequently than unsuppressed shots, but there seem to be some variables other than just decibels/tone that contribute to how deer react...otherwise they would run every time when hearing an unsuppressed shot.