When I ran into this issue on the rear fender of my 34 it had been cleared for several weeks and there was a flaw I needed to correct. I wet sanded the entire fender then applied fresh clear. Several hours later the solvent pop appeared. BarryK of this forum told me of my mistake and how to correct it. When I wet sanded the existing clear it opened up the surface and allowed it to gas off. When I applied fresh clear almost immediatly that is what caused the solvent pop. By placing the part in the sun for an entire day after the pop had been sanded out allowed the trapped gasses to vent completely then new clear could be applied without the solvent pop.