You may have a ventilation issue here due to adding a vapor barrier at the roof level with not enough ventilation. 

The company that operates the gas station is supposedly paying for the ongoing vapor/soil testing, etc.

It's amazing to me how many people don't think about this and how many houses we see with water issues that are so obvious on what's causing them.So, because you've ALREADY experienced issues, this may be a solution.A more comprehensive deal of digging down, putting in drain tile, perhaps a vapor barrier on the outside, would be a 'next step' in my opinion.IF you are selling and need that 'comprehensive' thing as a selling point, I might consider going further, however if you are holding for awhile and can observe results I'd go with my original recommendation. 

I got several other varying degrees like use 6-mil vapor barrier over concrete with a pad, or don’t use it and just put the pad down with the plank or don’t use padding and just put down the plank.

If you could not remove all affected wood in the subfloor - sometimes not possible, if strong urine/fecal matter made it to joists - you should have sealed everything which could have been done in several ways - polyurethane everything; poly vapor barrier; painting & 1/4" subfloor on top of old floor; etc.2.

@Yi ZhaoI would’ve knocked on the door and given them a vaporizer for their ganja so at least they can make the smoke odorless lol and after they praise what a wonderful landlord you are (with red eyes) tell them they can either Vape their weed in their apt. with that or walk outside if they need to smoke “flower” but they can’t do what they are currently doing.

You can also get it with or without a vapor barrier.

I think it's rubber.A local contractor says the top layer should all come off and then depending on the condition of boards below, that may need to be ripped up, joists checked, new carpentry, new insulation between, vapor barrier, etc.

Over long periods of time vapor itself can leave a thin Vegetable Glycerine (VG) residue that is easily removed with a warm wet cloth.

The steel, PSI, and vapor barrier will usually not be adequate.