When I have any problem with my thread/tension, etc., I check the needle and replace if necessary (what a small expense in the long-run), check the bobbin and re-load it if necessary, unthread and re-thread the machine. You can always take the time to clean and oil the machine just to be sure.

I also use one of those silicone (I think) washers in my bobbin case when FMQing. It helps with the bobbin tension.

I had a problem recently with the thread (top thread) breaking when I would FMQ. I took the machine to the shop and they GAVE me some thread silicone (can't think of the name of it right at this moment) and that took care of the problem.

Good luck. Hope you figure out the problem and get on with the quilting.

Becki