All machines that I've ever sewn on will eat the starting fabric if you don't use a leader, or a straight stitch plate, and/or hold the thread tight when you start. It's just the nature of the zigzag-capable sewing machine. I'm not sure what you mean, though, when you say "sewing over layers." Is that when you're in the middle of a seam and encounter another seam? If it's happening then, the only thing I can think of would be a dull or incorrect needle, like PlanoDebbie mentioned.