I remember your question about treats. You got lots of suggestions, unfortunately, that were from some inexperienced owners that recommended very unhealthy store-bought treats. Hopefully you were able to sort through that and are sticking with either the occasional slice of fruit or the Oxbow natural treats.
The reason your rabbit is refusing pellets is likely because he's preferring the sweets - just like a human toddler. The pellet food with sliced fruit in it is already over-dosing him with too many treats. Those mixed type of pellets provide more "treats' than they should have on any given day. If he is additionally being offered other treats, then you are raising a sweet tooth junkie!
Pellets should be plain pellets -- no add ins. Timothy hay should be unlimited -- this is THE MOST IMPORTANT part of his diet. He should be eating his body size in hay every day.
If a rabbit gets too many treats or too many pellets, he won't eat enough hay.
Given what you've described so far, I'd suggest it is time to "train" your rabbit to eat healthy. That is all up to you. You can begin by stopping all extra treats of any kind completely for now. He has to get out of the habit of eating all that sugary stuff.
At the same time, get some healthy pellets (some recommendations can be found
here) and transition him slowly to the healthy pellets so he no longer gets that mixed pellet food.
And always provide plenty of timothy hay during this transition. (If he's getting alfalfa hay right now, then mix in some timothy so he can get used to it). Refresh his hay twice per day to encourage him to eat it.
Have you introduced any greens to him? (carrots are high in sugar and are considered a treat) Greens come next after hay in importance but must be introduced one type at a time.
If you follow these suggestions, then that will will get him back on track and eating a healthy diet.