Rabbit won't eat before bed sometimes

A couple times now one of my rabbits would not eat in front of me at night. No favorite treats, no pellets and just running away when I get near. His brother happy to get all of the pellets lol. But both times he started eating without issue in the morning. Has this happened to others? Is it just a tummy ache or does he get grumpy with me sometimes? It scared me alot both times thinking I'd have to take him to a vet when they open. They are both 9 months and neutered. Still semi new at a couple months with me. Photo for tax!