I'd look at the countertop from underneath around the sink or under the drain pipe or around the wall where the drain goes in. Not sure how old the house is and otherwise hard to say without looking. Mold can get in under the cabinets, in the floor, and behind the walls where you can't see it.
A bleach/water solution on mold for a period of time should kill it but you need to address the moisture/humidity problem over the long term. You indicated it is a mold odor and so I assume not a sewer odor which would come from the pipes and is what a full trap is designed to stop. Some lavatories have an overflow hole in them and mold grows in them sometimes and usually stopping up the drain tail pipe down below and filling the overflow up with bleach/water will get that.
You should see where someone has allowed a drain to leak for years or under a toilet. Nothing but mold, mildew, and rotten wood that has to be cut out and replaced. A fun job. lol
Also are you sure you don't have a dead mouse, etc.(or rat in New York) under the cabinet or in the wall?
Also your kitchen drain should vent out through the roof up above. Take a garden hose up there and wash it out (with your drain pipe attached). Could have a dead rodent, bird, or squirrel in the vent or even full of dead twigs and leaves that are molding.