I had to return my first QE4 (bought in November) as I could not get the tension right for FMQ - the bobbin thread kept skipping and snapping. It was replaced in February with a new machine and at first everything was great. However when I tried to FMQ with rayon last week (something I've done a lot of on my Janome) I couldn't get it right. This time the top thread kept snapping!
Although the thension is supposed to be automatic, I think this is only true for 50 wt cotton.........