I wish you found the culprit. I'm going through this now. Newly renovated bathroom and I can't even use it because the odor is so bad. for me, I have a double sink vanity. The smell is 100% coming from the left side cabinet/sink but after deep cleaning, the smell just got stronger. It's as if the smell gets worse whenever I run water in that sink. And yes, it only smells in there, it doesn't travel to the hall.