These machines have so many "quirks" and are so sensitive to precision things. I think it is built in just to vex us. It is so easy to miss a step in threading and that messes everything up. Last night my machine was making a very small "popping" sound. I realized that I can't remember the last time I changed my needle (just lazy). The sound is gone. I think the point on the old needle was flat instead of pointy!
Sue