I think you are having a top thread problem rather than a bobbin issue. Check your threading again, and again. Thread from the top will bird's nest underneath if it is not threaded correctly or tension is off. Use a small test sandwich for trying different settings. Try using a No. 14 needle rather than a top stitch needle. They work best for me for FMQ on my Baby Lock Quilters Pro. Also, are you lowering the foot lever before you sew? Forgetting to do that will cause the top thread to "free wheel" into masses of knots underneath. Good luck!!!