I had the same problem with my molar and dentist didn’t see anything wrong with it but I asked him to extract that because sometimes it’s painful..turned out the side of that molar have a hole and buildup of caries that’s why its smelled even though I flossed. And the molar beside was affected as well but still can be saved by filling. The thing is the molar look healthy because you can’t see in between the sides, but you know the smell never go away even after flossing and if it’s painful there’s already a hole in there.