Sometimes it is as simple as the wrong sized/type needle with that size thread. You might have picked up some ball points?? If both machines are doing the same thing, try changing out the needle with another brand. Sometimes the dang needles are just no good, even when they are new. Then I would take a close look at the thread, is it a good quality? I am not being a thread snob, but just trying to figure this out .... Change threads, if you can.