walnut slab gone warped

[American0]

gosh, I thought I scored big with this aged walnut slab that's been chilling in a field for over a decade.
I brought a piece into my uninsulated shop, cut it for some end tables, and let it sit for a couple of weeks.

Then I flattened it with a router, gave it another two weeks, and sanded it down. I brought it inside my house to finish it in a nice, steady 62 degree environment, and bam! Two days later, my beautiful flat boards are all warped out of shape.
What the heck happened? And is there any way to fix this? Just doesn't want to waste it

 

[street.smart]

Sheesh, I think even though it seemed dry, the slab probably had uneven moisture pockets, and bringing it inside made it move fast. Try coaxing it back by letting it acclimate longer in the house before working it, or by sealing both sides evenly to slow the movement

 

[Guitarmaker]

It will have been full of moisture, in my opinion a couple of weeks won't be nearly long enough.

 

[Redmt]

I have black walnut trunks that have been air drying for 3-4 years. When I slab them out they still hold 20-30% moisture. It was slabbed into 4"x18"x30" pieces that took another year to reach -10% . Even then the took on a little warping.

 

[Alan]

Yeah, that’s classic moisture movement. @American0 field-dried doesn’t mean stable, and moving it into a warm, dry house made it release moisture fast and twist. You can try re-flattening after letting it fully acclimate indoors for a few weeks, but some warp is just the wood doing what it wants.