Possible suggestions:
Try rethreading the machine and bobbin. Clean with each bobbin or so. I've had lint build up under the plate and cause problems too.
Maybe different thread or larger needle, a top stitch needle works well-larger eye and stronger needle.
Machine need oiled often, I oil it every 2-3 bobbin changes.
How much tension on the quilt, should be able to grab the quilt on top, if you poke finger up from underneath.
Once take-up bar get fuller, raise it up so at least finger thickness between roll and bed of the machine.
Are you using a stitch regulator? If not try to keep and even speed.
Good luck, hope something helps. Sometimes it works after I walk away for a while, maybe we both just need a rest!!