Lop eared bunnies definitely can have a harder time cleaning out their ears, and with my Bailey, because she had hind-leg weakness, and couldn’t clean her ears, I got a solution from my vet and she showed me how to clean her ears.
The only thing is that the whitish gunk never smelled really bad – not like pus anyway. I also used solution, so I could smell the solution more than anything. Now I know you said that before it never had the bad smell, but now it does? Or did I misunderstand.
I know that this MUST have been covered, and I apologize for probably asking this before, and/or you having to answer this already (probably from the beginning) but are his teeth okay? Does he ever have any chewing problems?
Because it has that yucky pus smell, it would be a good idea to contact the vet you trust. She might be able to describe a “normal” ick smell or help you figure out what is going on.
Keep us updated.