Usually, if the underside of your project has a problem it is a tension problem, or threading issue. I would do the 'dollar bill' clean out of your tension disks. It there is a stray thread or piece of thread there the dollar bill should be able to dislodge it. Remove your bobbin and clean that area out, look for a stray thread that may have lodged in the bobbin or surrounding areas.
I always try a new needle, different thread, even wind a new bobbin.
I know how frustrating this can be so I sure hope something works for you!! Best of luck! :thumbup: