How long is your stitch length? Maybe you could lengthen it a bit, like to a 2.5 or even 3.0 when you get to that part of the process. I don't like to pull on the fabric as it comes out the back of the needle, but you might want to tug it a little with a steady pressure to help it along. I've made over 275 masks so far and haven't had much of a problem with my Bernina 570. But I"m still looking for the perfect pattern!
Leslie