John,
Rather than pin holes I suspect you have gas bubbles (gassing out) from the wood. Since the previous epoxy layer was cured enough to prevent gas ecapeing, it was trapped and lifted the epoxy and glass, resulting in rather large bubbles. 20 degrees may not make the wood expand much, but it will certenly make the gasses within the wood expand. You can fill the bubbles by injecting epoxy into them. There's no need to "check" for pin holes, you can pretty much figure they are there. Subsequent epoxy fill coats and varnish will fill them.
Jerry