Two things I found can cause this issue.
1. 2nd color isn’t being shot hot enough on to 1st color.
2. the 1st color you shot has sat around long enough it gets oily residue.
These can be fixed by shooting the 2nd color hotter (375 or so) as well as cleaning your 1st color side you will be laminating to with 90% rubbing alcohol. Also hold pressure.