With FMQ, unless you can perfectly time your machine as it does with straight stitching, the bottom thread will always pop up. Did you loosen the top tension for the mono-filament thread?? If you can't, you might want to increase your bobbin tension. I have a Bernina 1530 which has a small hook with a hole that can increase the tension for heaver thread on top. Good Luck and keep experimenting until you have solved your problem