Mystery smell is back

[Remmy Vernon]

This is a small one bedroom unit, ground floor, no unit above it. (approx. 600 sq. ft.)

When tenants moved out there was a bad smell. I could not out my finger on it. It is not in the bedroom or bath, but in the kitchen area, which is open to the living area.

What I tried:

New paint everywhere

New carpet

New fridge

Scrubbed grout in kitchen till it looked new

Painted the inside of the cabinets

Ran ozone generator two times back to back

After all that, smell appeared to be gone. Rented it out. Went back yesterday because of an issue with the stove, and the smell was back. WTH. Tenant has not complained though, but it really bugs me.

I simply can not pin point the smell to anything. It almost seems like it is 'in the air' in the kitchen.

It can't be something dead, that smell would go away eventually. It doesn't smell anything like mold and I checked everywhere for leaks prior to renting it out. No signs of leaks or water damage anywhere.

Adjacent units have no smell. Common area hallway no smell.  

I am stumped.

Now, I am going to replace the stove because of the issue with an element not working. I know I can fix it, but I am hoping that maybe there is some old nasty food or grease stuck in the stove that is making the smell. 

Any other ideas??