2 chess pieces done back to back with 2 results

I downloaded a knight chess piece, and went thru everything to create tool paths, for a roughing pass, a finishing pass, and pocket path at both ends, and sent it to gsender, the pocket path was to cut down to .830" , which it did fine on a test piece of spruce. mounted a piece of walnut and started the pocket path and it cut down to about .250". It was too unstable to finish the cut. Any ideas before mounting another piece of walnut. By the way both the spruce and walnut finished the rotary surfacing fine’ and the spruce piece finished all paths fine.

@jareed58 Just a stab in the dark. Were both the test piece and the walnut the same diameter?

You used the same gcode for both the test piece and the walnut piece, correct?

Yes both were rotary surfaced with the same dimensions, 1.95"