If the exact symptoms happened on kibble and the week before starting raw I would say it looks like some sort of bug/parasite. It does also sound like giardia or one of the intestinal bugs that can linger and intermittently show symptoms and false periods of recovery. Does he swim or paddle in any stagnant water or creeks?
The only other thing that it may be if it's not a parasite/GIT infection is something he has access to and eating in your garden, at the park or on walks....something even sprayed on grasses.
The smelliest of the poo seems to indicate that it is more likely the first possibility.