sounds like you got a MC imbalance OR it wasn't as dry as you expected. A lot of variables go into a correct answer BUT this is the most common I see when drying or building with slabs which usually caused from imbalanced air circulation.
1) NEVER put forced air directly to one side. One side dries faster than other.
2) ALWAYS be sure your 8" or more off floor, table, bench, wall etc, etc AND air flowing evenly into the sides as to flow thru.
3) Keep fan away and not directly pointed at surface/lumber. Drying too fast is just as harmful.
I think you can save IF corrected soon by elevating (#2) and slow balance the MC by indirect air movement..
Sometimes reslicing a slab imbalances as internal MC is 95% of the time different than external and needs time to rebalance.
Your rained on is also a concern BUT usually can be rebalanced IF proper steps done.
I recently proved to a builder how shop MC/RH's can create havoc on warpage by not air spacing above benchtops enough. I AD the pecan lumber over several years and was relatively flat at purchase. He started his slab tables then called re a concern of slightly warping. After consulting and going to his shop I seen and explained 3/4" air space is nearly NO air movement. We raised to 6" and let acclimate a week and it flattened back to original flatness.
I think the rain then a more direct towards one side air movement (without further info) and imbalance air flow may have been your culprit. 98% chance it will reflatten once properly acclimated evenly.
My website hasn't been updated in a long while BUT has pics to show my sawing and drying knowledge.
I hope all turns out well.
Tim