I am not sure what kind of resin I used, I did sand the glass. I figured out that the culprit was the wetsanding. Supposedly one is discouraged from wetsanding bondo for that exact reason, or at least that is what the guy at the store said. Who knows. Thanks for making me ask that question.
what kind of resin are you using? did you sand the plastic you are glassing to? just trying to shoot ideas out to find the cause of the issue for you, let us know how it turns out and what was the culprit