Mods probably will merge this with the other thread but the answer is everyone is different. No apparent logic, no method to their madness. For example, I have always been successful at ATL while you are 0 for 6.
Actually only missed a couple times since last year but one was interesting, a new data point. Standing in PreCheck line at LAS with about a dozen pax in front of me. No one cleared for PreCheck. Asked the TSO if PreCheck was down, he responded that it was working but no one on my flt qualified. Never heard that before. Don't know if it was because of some special pax or whatever but sure enough, a guy a few pax behind me cleared.
Bottom line is it works better for some than others. I guess that is the "randomness" that TSA is looking for.