Yes, it's an effective S-Trap.
S-Traps are known for siphoning and new construction only allows P-Trap installations. You have a long horizontal run after a P-trap that prevents the siphoning effect.
The outflow on an S-trap is a straight drop which under high flow conditions can allow more water to be drawn out of the trap than is needed for a water seal, hence the sewer gas.
The short term solution is to allow the sink to completely empty, then run a quart of water down the drain afterwards to make sure there's enough water down there.
The long term solution is to figure out how to re-plumb so you can install a P-trap.
On checking the vent stack, I've had to run a long pole down them to clear out paper-wasp nests.