I’m glad he perked up! My go-to when a bun is off are to start with fluids and simethicone. If that doesn’t help I feed them and give metacam (if I have it and the bun has had it before). If I’m unsure I usually just do a very small amount of food and see how that goes. It sounds like your intuition was the right move in this case!

Some buns are just really sensitive, unfortunately. My Bunston was like this, where he would just get these random “attacks” of poor appetite and gut slowing. You could try going on a hay-only diet for a while to see if that helps? Some buns are sensitive to pellets or a specific green, or a specific pellet ingredient. Or you could go hay-only just around molting time to see if that helps.

Do you have sub-q fluids? Those can also be really helpful as a first think to try at home when a GI episode hits, and are unlikely to do harm. Myra used to get these bouts of pain with molting and sub-q fluids would perk her up almost immediately. Since these things happen regularly with your bun I would ask your vet if they can prescribe you a bag of fluids and show you how to give them (one bag will keep for a very long time, even if you use some of it).

Personally, I don’t hesitate to syringe feed when a bun won’t eat, unless I have a clear reason suspect a blockage (not just molting, but something like they’ve eaten a large amount of some foreign material). At the rescue I volunteered at, all the senior staff all feel the same and my old vet said that is usually their first course of action even when a blockage is suspected, because the goal is to try to push the blockage through. The only time they really wouldn’t was in a case of true bloat. Obviously that’s my personal choice and it’s not without risks, but there are also clear benefits to syringe feeding right when a gut slowdown is suspected, so I feel it’s worth the risk.