Suddenly transitions have become unreliable for me. When I move up from one space to another the transition will sometimes show as coming in from the side (I use Slide). This was never a problem until about a month ago. A restart fixes it for a little while, but eventually the directions of all the Slide transitions appear to become random.
I do always end up in the correct space - it's just the transition is the wrong direction.
10.11.6, 2012 Macbook Pro, with external display attached, 9 spaces in a 3x3 grid.