I see this at times in r114 so it may not be a bug in r116, it may be that the way the detection is occurring and where the snail is happens too late for it to turn around. frame rate, position of the marker near the edge and a couple other things could also cause this. Try adjusting the location of the edge marker (move it farther in) or possibly make it a bit bigger as well and see if that helps at all. I would recommend trying in the last stable build (r114) as well and see if you see the same issue. Though you will have to start the tutorial over as the r116 built capx will not work in r114.
hope this helps, thanks!