Sorry I'm late to the parTaY..
Here's my two cents worth:
You must stop all treats, pellets and greens/fruits.
Hay and water only for a week straight, no gives (I know how those sweet twitchy little noses can make you cave, but don't do it
)
No alfalfa anymore, that's for baby buns.
My last girl was THE PICKIEST hay eater, I had to get 4 different kinds of hay and rotate or mix them.
For hay I purchased: Timothy, orchard, oat and also oxbow hay stacks with chamomile.
The hay stacks always got her eating her hay again. When you start to re-introduce veggies/fruits back in, do so 1-2 at a time once a week and see if that helps. I'd also stick to oxbow pellets but only ever give up to 1/4 cup a day. I give theirs at dinnertime, but make pellets the last thing you re-introduce.
My little fella has what we call intermittent soft cecaltropes or ISC. He is a doublemane lionhead so his fur is longer than other buns and so he gets clumps stuck to his underbottom if I don't notice he's got a flare up of ISC.
You can read about it here:
https://rabbit.org/intermittent-soft-cecotropes-in-rabbits/
But when in doubt, always take bun bun to a vet for a check. I understand your bun is young, but it may be having tooth spurs which would cause bun a great deal of pain when eating, so they don't want to. There could be an underlying condition.