4years ago I milled 3000 bd ft of white oak from my new home site. I had the Amish in my area air dry this rough lumber for 3 months and the kiln dry it to 8% and mill it into hardwood flooring. Then I stacked it in the home I’m building where it sat for 18 months at 60 degrees constant. Then I installed 2000 sq ft of it on the main floor of this same home. Again I waited 6 months and then had some professionals sand it. They did a beautiful job. When they departed 3 days ago the entire floor was as smooth as glass. At that point I applied a solvent based sealer stain (wipe on / wipe off). It looked beautiful. Now 24 hours have passed and the flooring is no longer smooth. When you pass your hand across the boards perpendicular to the edges you can feel virtually every edge on every board in the house. The outside temps here in Nashville have been below freezing. The house is heated to 60 F. I have not installed my humidifier yet. The flooring board widths are a 3, 4 and 5” pattern. I am pretty confused about why the smooth floor now appears to have cupped boards. The current humidity in this house is 31%. If anyone can give me an opinion on what may be occurring that would be very helpful. Thank you for your time. Jim

I would ask your sanding guy to look at it first. And your sure it was a solvent base sealer stain? No cupping prior to sanding?
Did anyone check the moisture content of the sub-floor and compare it to the flooring MC?
That Rh is pretty low. I'd humidify for awhile before sanding again. But I'm not a sand and finish guy, so others here may have an idea on whats happening.

What's below the first floor? Basement or crawl space and what are the conditions there? Cupping usually indicates a humidity imbalance between the room(s) where the flooring is installed and the area below (basement or crawl space)......humidity in first floor room(s) is lower than the basement/crawlspace below. That's pretty fast for cupping to occur. Get all relative humidity conditions under control and give it some time.....the cupping may resolve if it's not too bad.