I used to have a rag rug shop where I had as many as 5 girls sewing the strips together. We had a great deal of trouble with thread, machines, breakage, until I bought nothing but Berninas and Gutterman thread. Finally it was explained to me that the humidity has a great deal to do with the thread actually untwisting. Gutterman wasn't as bad and a Bermina will still sew until you burn up the motor.
I'm thinking of starting FMQ so this discussion is most helpful.