Your bun's diet must compose of 90% hay. They need a huge amount of fiber. The remaining 10% is pellet, green, fruits and some treats.
The hay is also necessary as it helps them wear off the on growing molars in their mouth. If your bun doesn't have hay stem daily, eventually his molar will overgrow, then you need to have teeth surgery. Hay stem greatly reduce the growing of molar (teeth)
If there is more than say 7% pellet, then your bun will eat the pellet, not the hay. As they love pellets. So you need to control and downsize the pellet and focus primarily on hay, especially hay stem. You always give an unlimited amount of hay at all time, far more than enough that should last for days, then refill them when they run low.
To make matter worse, your bun will have other problem, such as GI stasis, that's a guarantee, I had a bridge bun Little Happy who was just like that. You need to gradually downsize his pellet supply, and increase his hay intake.
Take a bundle of hay and hold it in front of his mouth, he will bite off some of it, and eat some of it. Off than that, at ALL of his usual spot that he sit around, put a bowl of hay there. In my house, I have 5 pot of hay in various part of the house, all favorite spot of my bunnies