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┬árather 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┬áthe 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.