Having birds nest on the bottom of my project when stitching over multiple layers, I'm using a denim needle and even changed to the yellow bobbin case and still having the same thing happen. Are you able to see the attachment? Can you tell me what I'm doing wrong?
Noting that it's spring, which is normally when birds are nesting, Jim says:
It's really hard to see anything from the picture, but if it's a dense design you may need a smaller needle. Changing to the yellow dot case won't really make much difference, because it increases the bottom tension. Your problem is either insufficient top tension, or more likely too big of a needle hole. If the design stitches fine over a single layer, then you may just need to slow down the machine at the trouble spots on multiple layers. Also make sure your fabric is taut within the hoop and well stabilized.