mammab

I am trying to quilt a small quilt using the stitch regulator on my machine. It stitches fine for awhile. Then it randomly skips stitches, sometimes 1 or2 and sometimes an inch long section. Then it starts stitching correctly again. I have changed the bobbin, changed the needle, cleaned the sensor or the foot. Anybody have any ideas. The last time I had this problem, I thought it was from chalk dust on the sensor, but this time I have not marked a pattern. I hope I attached a couple of photos.