On Tue, 29 Jan 2019 15:27:42 -0800 (PST), DerbyDad03
wrote:

I'm trying to flatten the
long twisted boards first and use the thinnest of the resulting boards as
my final thickness. Since one end keeps coming out screwed up, I'm simply
trying to determine what is causing the problem.

Are you shimming under the boards anywhere they are not touching the sled?
If one edge is not touching the sled I'd want a shim every 12".
--
Jerry O.