Unglued spot over concrete slab that isn’t level

Q: My husband is installing our engineered wood flooring by gluing it down. We have a concrete slab with linoleum, which he coated with a concrete leveler rather than remove (we didn’t want to mess with asbestos). We are about 1/3 finished with our front room and when walking on it, I noted there is a spot where the floor is uneven slightly and the wood is not glued down.

When I stepped on it, the two boards over this uneven ground ever so slightly sunk and made a crack/snap noise. It is too small to crack the wood but enough that when walked over will make a noise every time. What can we do? I don’t want to have to pull up everything we have down already to level the floor. Can we nail each board into the concrete, using a drill to make the hole first?

He also suggested actually cutting out one section of the floor and replace it after leveling the floor? That doesn’t sound ideal to me, because I know it won’t go unnoticed.

A: Drill a small hole and use an injectible adhesive. Any number of adhesive manufacturers likely make something suitable for this. Perhaps Bostik Findlay or Vermeister etc.