Yet Again..
Remove the dust cover from the tool carriage and blow out all of the dust and crud that's accumulated there. Pay special attention to the blade holder up/down mechanism. It doesn't take much contamination to alter the cut quality. Also, make sure the little ball bearings in the blade holder are sufficiently lubricated. Usually a bit of silicone grease on the tip of a toothpick does the job nicely.
From the number of complaints about dubious cutting and the number of times I've given that same advice sometimes it seems I'm the only person on the planet who knows about these things.