The smell is 100% due to McKinnon's; and its because they do clean their dumpsters w/ high pressure water, which then runs down into the storm drain in the parking lot and turns rancid there. That's also why the lot is always slippery; since the runoff leaves a lot of grease behind.
Not sure why its worse recently; which i have also noticed. Maybe the drain is getting more clogged w/ grease.
Not sure what the city can do about it; I think its allowed to clean their dumpsters in this way.