I have the 2010Q. How’s your bobbin tension? Do you happen to have a TOWA gauge? Do you have fuzz under the backlash spring in the bobbin case? Have you put a thin pin under the bobbin case tension arm and blown out any fuzz with canned air? Rethread the upper machine. Are there any burs in the checkspring? (The little spring in your tension dial). Make sure your bobbin is in the right way.
These are just a few ideas. Hopefully you’re able to pinpoint the source.