Pin holes are caused by dust particles on the board when hotcoating. The dust prevents that area from bonding. Pin holes will allow water to get into your board.It is best to blow off the board with compressed air and wipe down with denatured alcohol before hotcoating.You can also drag piece of masking tape, sticky side down, over the board to pick up dust particles.After hotcoating walk out of the room and don't touch the board. Moving around the board may kick up dust which might settle in the board causing issues.To fix the pin holes sand the board to 150 grit and either re-hotcoat (glosscoat) the entire board or just do small epoxy patches / fills over the pin holes and sand them flat after cured.