My wife has also been complaining about an odor in the kitchen, and
said she began to notice it shortly after the flooring was installed.
I have noticed it myself, but I just figured it was the glue he used
to install the flooring.

I am not sure what to do about this lump. Does anyone have any
suggestions what could cause a lump like this, and how to get rid of
it?
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I hope you have an extra piece of flooring to insert. It sure sounds
like the obvious, some sort of debris caught under the flooring.

Call an new floorer if you can't get the original guy to come back. It
might a case for small claims court also. Document everything.