that actually definitely sounds like shoulder mobility! pretty much every olympic lifter starts like that from what i've seen. i guess i could make a video on how my coach used to fix it, if you're interested *shrug*. it's quite an uncomfortable adjustment. kind of the same feeling when you first do behind the neck barbell shoulder press.
it usually is considerably more time consuming to adjust for someone who already has muscle built in the shoulders, traps, lats, rotator cuff, due to the tightness/lack of mobility they inherently have relative to a weightlifter due to their strength training. not a bad thing, though, just a thing.
but meh doesn't seem like it matters, anyway eh! if you can do other variations of fsq for reps at > bw, then who cares i say!