Had a boarding pass for a UA flight departing T7. Wanted to go through TSA Pre Check security at T4 since TBIT doesn't have Pre Check for the purpose of spending some time at the *G lounge in TBIT. Never had an issue before, until this time.
Walked up to the Pre-Check AA staffed (contractor?) person at the bottom of the escalator in T4 and she tried denying me entrance. Literally an interrogation and I was very polite until about the 4th question when I started getting annoyed. She tried questioning whether my boarding pass was valid (I'm ok with this), tried questioning the app I was using (still kinda ok since she probably was used to AA boarding passes...), tried questioning why I wasn't in T7 (um, sure?), tried questioning why I wasn't going to a lounge closer to T7 (ok...) tried questioning why I was traveling alone (really?), tried questioning why I didn't have more bags (was traveling very light, just small duffel). At the end of the last question, I interrupted here a little and was like, look, per airport policy, I'm allowed to go through security at any checkpoint if I have a valid boarding pass, and this is a valid boarding pass. If you disagree, please tell me now else I'd like to go see the TSA agents for screening. Her response was: "I know airport policy, I work here!" And with that she let me through.
But all in all, you're still able to get into TBIT via T4 Precheck. Just a heads up that they might try finding any reason for you reach the security checkpoint.