Dennis,
I have a 100 TSX fail to expand on a pronghorn from a .257 Weatherby, and Eileen had one from the same lot fail to expand (or at least not open as much as it should have) from her .257 Roberts on a mule deer as well. The .257 Roberts deal could have been blamed on the lower velocity, but the range was only 50 yards and the muzzle velocity was 3150 fps.
But we haven't had any problems in the .257 Roberts, .25-06 or .257 Weatherby with plastic-tipped monolithics, whether the TTSX or E-Tip. The game taken has included a bunch of antelope, whitetails and mule deer, and one elk. And the elk was taken with the Roberts, not one of the larger 25's.
