Something's gone off inside my catsuit and washing isn't fixing it

I have a catsuit that has developed a smell on the inside. Not the usual rubber smell, something sourer, and it has survived two washes.

I wash it the way I wash everything: cool water, small amount of mild soap, rinse, hang to dry. It comes out smelling fine while it is wet and then within a day it is back.

Has anyone dealt with this? Is there something that clears it out properly, or is a suit that has got to this point on its way to being binned? It is the most expensive thing I own and I am not enjoying the thought.