I've used the TEZ for years. (250g) and have never experienced it not expanding that I am aware of. That being said, I've never recovered a bullet. The closest shot I had was about 10 yards. He basically death stumbled for about 20 yards and that was it.
I can't really explain what you experienced. I will say though, I do prefer the Expander over the TEZ but I have 100% confidence in the TEZ.