When that happened to me, I discovered that for some unknown reason, I had started putting my bobbin in backwards. I was very carefully putting it in backwards. Finally, I got out my manual and went step by step through the entire process and figured out what I was doing. This was not a new machine, there was no reason, but that was it! Weird! It seemed to only cause a problem when FMQ. Didn't notice on straight stitching.