I know warping can be caused by internal stress, but not sure if that applies to wax (in this case green File-a-wax)
The part is 10x80x140mm. I taped it down with ~4mil double-sticky tape. I faced it with light feeds and speeds by hand on a Taig. Not it's not a noodle! My similar aluminum plates are not warped.
The warp is a centered bow. The bow in the finished part is about 5mil, totally unacceptable.
I tried to flatten it with heavy weights on a 3D printer bed that I raised to 70 c and slow cooled to room temp. That seemed to work at first but then the bow came back by the time I tested it on my surface. I didn't want to go higher temp because if it starts to melt, it's ruined, and I can't find any info on the glass-point of machinable wax anyway..

The only thing I can think of (other than residual stress) is the squishiness of the tape because it will squish more from downward pressure at the edges than the center. But the tape can't squish that much.

This is recast wax btw, but the wax was fresh blocks because I needed a bigger plate than my inventory. A bread-loaf baking pan with Baker's secret coating completely releases on it's own, it just falls out because the shrinkage is so high (I slow-cooled that overnight also). From that I band-sawed the pre-blank stock to start with.

Any ideas would be appreciated. I could start doing experiments but that would get tedious fast.
tbanks