are the two fabrics about the same weight and texture?
have you already tried the following? if you haven't, try each thing in turn. not all at once. it's possible your needle is the wrong size for the thread you're using ... or vice versa.
switch to a different size needle
switch to different weights of thread(s) in the top and/or bobbin?
flip the strips so the fab that was on top is now on the bottom?