Oh dear, I feel your pain. My Bernina 440 had to go to the shop for skipped stitches during FMQ. It was the timing and it is now good as new. The technician asked if I had check my other stitches and I had only checked my walking foot( skipped) and my FMQ ( skipped) and regular straight stitch. He said it wouldn't zig zag at all. Try your other fancy stitches and if they are skipping too, you will probably need the timing fixed.