I worked for what seemed hours one day trying to bird-dog each and every possibility for missed stitches in FMQ. Turns out my needle was slightly bent (no doubt from pushing the weight of the fabric through my then small harp space). Wasn't discernable by the eye, but laying it on a flat surface and examining with magnifier, sure enough - it had a slight bend in it. Went to a bit heftier needle and problem solved. Might be worth a try.