It may not be that Theo is sensitive to the pellets, but that those pellets have a contaminant or toxin making Theo sick. And continuing to feed them could not only continue causing him to get sick but could possibly result in irreparable internal damage and even possibly be fatal. If there is any chance that those pellets are the cause of him continually getting sick, please stop feeding them immediately.
Something that you don't understand about bulk feeds like that is they don't always use quality ingredients, which means there is a higher likelihood of something going wrong with them. There are instances where contaminants or toxic amounts of vitamins have been inadvertently added during the mixing process and this has resulted in causing permanent organ damage and the death of hundreds of rabbits that were given the feed.
It happened in my state a few years ago where toxic levels of vit D caused the death of hundreds of rabbits due to causing organ failure, and I also have a friend who's rabbits were adversely affected by a bad batch of feed with toxic levels of vitamin A, where either her does couldn't get pregnant, or when they finally did, all of her newborn baby rabbits died within the first few weeks from hydrocephalus and other symptoms of vit A toxicity. These things don't happen frequently, but they do and can hapoen, and need to be taken very seriously.
