I built my house 13 years ago and installed 3/4"x 3 1/4" tongue and grove solid maple over 3/4" plywood subfloor with asphalt impregnated kraft paper in between. The flooring acclimated in the house for two months before installation and was installed for two months before it was finished.The crawl space is covered with a poly vapor barrier. I let the flooring finisher talk me into using a waterborne polyurethane and have regretted it from day one. Previously I had used Swedish finishes on all wood floor installations but had relocated to California and went with local recommendations(except if I had really been listening I would have gone with engineered flooring because relative humidity can get into the teens in summer and "real" wood can't handle that).
The problems showed up within a year with cupping and gapping. Going to sand it down and use Bona Drifast oil sealer and Bona Traffic HD. My question is: Where did the cupping come from and will it come back? The gaps are understandable with the changes in humidity. But the flooring was dry when installed, dry when finished and with vapor barriers should not have had a differential in moisture to cause cupping. My theory is that a inferior polyurethane was used. Don't even remember what it was but it was a commercial product, not something off the shelf from a big box. Will Bone Traffic HD stop the cupping?

Could just be dry cupping, not the finish. Whats your current ambient rh?

RH was 35% yesterday,55% today will be around 25% next month.
What is dry cupping? I thought cupping was caused by a difference in moisture content between the two surfaces of the flooring.

Hmmm, well dry cupping is when the top is drier than the bottom of the plank. Often referred to a moisture imbalance form top to bottom. Often happens when the rh is in the teens like you said, and the gaps would coincide with the dry cupping.
With your rh up now it may take awhile to settle down. Whats the rh in the crawl space? Can you pin meter the subfloor down there?