It would be foolish to suggest anything without knowing what type of finish you have.

What type of finish do you have? Is it hardwax oil or a traditional polyurethane? How old are the floors? Where in the house is this occurring? How many of these spots are there? What's your cleaning routine and what products do you use to clean your floor?

Polyurethane. Relatively new flooring installed a few years ago. We use bona to clean the floors.

They look like water or oil stains. Polyurethane is very good at keeping most moisture out, but it isn't water proof...it is ranked as water resistant. Water, if left long enough, will penetrate through the finish and then mark/mar the wood. Oil will do the same thing.

Once liquid gets underneath the poly (and hits the wood) it is very difficult to remove stains that are brought about because of it. The fumed finish also creates the appearance of staining (simply because of the colour).

At this stage, there is little that can be done.

Can you isolate those spots and tape off the boards to perform isolation repairs? Also are the floors cured? That’s huge because doesn’t matter the finish if it’s not cured it can’t protect 100% as advertise.

It looks like an oil finish. Repairs can be tricky for some finishes.