The National Wood Flooring Association says that a gap of up to the thickness of a dime is acceptable for normal seasonal movement within a wood floor. The relative humidity in a home drops during winter because the air is dried out from a forced air heating system. One of the issues with seasonal movement is that it really tests how well the finish is adhered to the boards.
I have recently been talking with a homeowner in NC who is having problems with white lines syndrome and poor adhesion of oil based polyurethane to a walnut floor.
Looking at the pictures and having seen this problem firsthand, the floor is going to have serious issues with peeling finish. This is not a “normal seasonal movement” problem. It is an operator error issue regarding preparation and application of finish. The oil based polyurethane is not sticking to the boards.
Unfortunately, the only fix is to re-sand the entire wood floor. The floor is 3000 square feet and that will not be a quick problem to fix. The wood floor contractor tried to pass these problems off as normal seasonal movement, but that’s just a last ditch effort in hopes that the homeowner will buy that explanation and go away. These types of problems do not surface immediately, so sometimes choosing the wrong company can cause real issues with your time and countless headaches after you have “the keys” to your brand new floor.