Change of diet and to much of anything can kill a rabbit quick also we found rabbits do not do well if raised in cages and then raised on the ground seems like they have a weaker immune and get sick more often.
We would keep him away from the other rabbits for sure for a while. He may also have a wool block it occurs when the stomach fills up with rabbit hair. It can be a partial blockage, complete blockage. Rabbits with wool block will not eat as much.This can cause a lazy digestive system , constipation and gas build up.
Not a vet just raised a few rabbits.
Good luck with him
Is it normal for a rabbit with bloat to last this long?
Most rabbit can die with bloat after just a couple days. Any digestive problems we had with our rabbits we just fed them their hay and water until the problem resolved.No greens or pellets but that is just what we did.