Weezy Rider

I haven't had that problem (2140 and 44) but I don't use the thread cutter for anything, even embroidery. I've turned it off.

I either hold both threads to the back, or start on a scrap piece of fabric.

Have you checked your bobbin tension or even the case? I have some old cases that have snags in them. Did the serviceman clean all the old threads out of the bobbin area? How about the top tension?

Try what they suggest for Free Motion Quilting - take one stitch, pull up the bobbin thread by using the top thread, and then hold both threads to the back. If it still snags, there might just be a burr somewhere or even needle or timing. A burr on the plate can cause problems. Crocus cloth can fix that.

If you are quilting - get a single stitch plate. You can temporarily make the hole in the zigzag plate smaller with tape to experiment.

How old are your bobbins? The plastic ones can get out of round. The Pfaff name is supposed to go on the top of the bobbin winder spool. (according to the book - I use generic Pfaff bobbins along with branded Pfaff) I've had some go wonky.

If you are winding a bobbin through the needle, check the threading and try filling bobbin from the top. Use a recommended Schmetz needle and the right fabric for that needle.

HTH.