I also have the same machine and have episodes like you just did. Sometimes the thread will slip out of the take up lever causing problems....was suggested to me to thread the take up lever in the opposite direction - it does help a bit. I also find that sometimes the tension discs get "funny" and I have to turn the machine off and on again - seems to fix it. I don't care for the problems, but they only happen when doing fmq. I find that if I check the tension on the top thread before starting that it helps (with the presser foot down you shouldn't be able to pull the thread through).