This is such an interesting topic. I can’t say I’ve noticed a bad smell with any of my current crew but I could probably pick who was who blind.
My first OTTB had such a distinct sweat smell - it was a very sharp, almost dirty smell. I could always tell which blanket or saddle pad was his. I would always have to wash his stuff more. I never got an answer for why. He didn’t have any health issues up until the end, and he lived into his twenties.