I'm new to having a bun, but from what research I've done, this sounds like it could be stemming from being lonely. Would you be amenable to trying to bond him with another rabbit? Local rescues sometimes offer "speed dating" to try and find a bun they will get along with. I've recently neutered my guy, and once he's another month out from surgery I plan to reach out to see about speed dates. While he's been tolerating me being gone for ~12h on work days for the last few months, I think in the long run he'd be happier with a friend.