You are spot on.That damage is two fold. The first is by carpenter bees boring into the wood to lay eggs. The second and most damage is by a woodpecker destroying the wood to get to the bee larvae.
I had the same problem till I replaced all my wood railings with pvc railings.
it was definitely night, she heard a racket on the porch but assumed it was the cat. She said it DID sound MUCH bigger and noisier than Twitch but just kinda wondered what he was doing.My guess is a woodpecker after carpenter bees but not at night. Are you certain it was at night? It would only take a few seconds for them to that. I watched one tear up a pressure treated 4x4 and do twice that much damage in less than 10 seconds.
Nothing in the world is better than watching TV in my living room when one of those guys is hammering on a well dented chimney cap trying to attract a girl friend. Said nobody ever.....Nah, woodpecker could never do dat!!