Looking at the outline on the stock, I’m also leaning towards what Jeff said… gcode error. Looks to me like it’s running the inside of the contour, not the outside… or some issue with the CAM not using the correct bit radius or sumpn.
Post the gcode here if you want folks to help rule that out.
(Edit… well after reading the whole thread, I now wonder if it is just machine flex. Removing material 5x faster can increase loading substantially depending how it is done. You may have to change your method of speeding up the cut. Just using a deeper cut alone only goes so far. You might try using smaller step downs and increasing feed rate instead.)