Uneven upstair room and floor leveler?

[Robert Hernandez]

Hello BP family

Recently bought a quadplex. And one of the units I went into has an issue on the second floor where one of the room hardwood floor is wavy and I can feel like a speed bump in one spot in the room, is that like a foundation beam? Visually it is kinda hard to see. The bottom floor looks and feels good no alarms of major foundation damage or anything. Doors and window close fine. That room has raised hardwood, AC went out in the summer and was vacant. So I am thinking that the hardwood is buckled due to lack of expansion. So I plan to replace the wood anyways, but the floor may be uneven.

I plan to install vinly again. Bt would the speed bump be an issue? Or can I level the wood somehow? Also, since it is on the second floor is a self leveler concrete very bad or can damage the property since its heavy and will be upstairs? 

Anyone have experience with using shingles for levelers, i heard about this options and it looks like a good alternative? Thank you

The house is built on a slab and the bottom floor is even. Just the upstairs kinda concerns me.