Recently (April?) Fons and porter had article on fmq and described this....it happens to me too. The lady said as you fmq the needle bends/flexes a bit because everything/fabric is in constant motion and thus the needle/thread timing can not catch resulting in skipped stitches. She said slow doen. There might have been a needle size change suggestion too. It was a good article. I read it in the bookstore but have been meaning to get a copy of it. Hope I described it ok.