First of all, hardwood flooring is real wood and as such it is not going to be as stable as some other products such as laminate. I always say if it’s natural expect it to have flaws. Some people want perfection in their flooring to which I say buy a fake glued up material that looks great and will not react as much to its environment. ¬†Most likely your hardwood has gaps because it is drying out. Dry wood shrinks and gaps appear. Some homeowners add humidifiers to their furnace to try to maintain certain conditions but I feel it is part of what makes hardwood unique and it is totally fine. The gaps will shrink again in the spring when the humidity comes up in the outside air.