See Map scrolling is choppy/sluggish & stuttering
I think it’s a frame pacing issue. The FPS counter jumping all over the place is probably because frame output isn’t consistent. If the FPS counter uses a very narrow resolution (e.g. last 2 frames divided by time elapsed) then it will jump around like crazy while the game is trying to output 60 fps on average.
I’ve been testing for over an hour to no avail. I’m not touching this game until it’s fixed soon, or I’m getting a refund.