Traps eventually dry out, letting sewer gasses back into the room. You might want to consider replacing the P-traps with HepVO waterless valves
. They have a silicon, duckbill one-way valve that doesn't depend on a tiny pool of water to block sewer gasses.
Since the HepVO is self venting, you can also remove the AAVs (Air Admittance Valve) and cap or plug off the pipe they are on. AAVs are a valve that replaces the vent pipe that runs to the roof and are popular in RVs because they are cheaper and easier to install, especially where it would be difficult to run a vent pipe to the roof. Sadly, AAVs frequently fail and are a source of mysterious sewer gas odors in a home or RV.