Each floor is unique and as a result, may require further attention prior to floor's sanding and finishing. There are two methods of floor Gap Filling. The first method of glue/ epoxy-resin mixed with saw dust is the cheaper method but will over time (2 - 3yrs), slowly shrink due to thermal expansion. This is because of the flooring boards contracting and expanding during seasonal temperature variations. Hence, it is a short term solution and may not solve the problem as you may need to repeat.

The second option requires more aptitude on the flooring renovation specialists behalf, but is permanent and recommended for that professional wood floor finish. This method involves cutting MDF strips and, gluing/wedging the strips between the floor boards to eliminate those draught allowing gaps.

Flooring on Wikipedia