What your stitches are telling me is that your bobbin tension is too tight. I'm not familiar with the Janome so check your manual for FMQ, with the Pfaff the top tension should be set to zero. If your machine has a bobbin casing, loosen the bobbin tension a little and see if that improves the stitches, continue to loosen until the bobbin is not pulling your top thread through. If your machine is one of the 'self regulated/can not be adjusted' type then I don't know but certainly start with your manual. This pulling can also happen when you are moving the quilt too fast relative to the speed of the sewing machine.