At the moment, I'm not able to reproduce the problem, as using CTRL for PTT works for me consistently (with prolonged presses as well as rapid presses). I would normally not use a modifier key (CTRL, Alt, Shift, Windows) for PTT as those keys are highly utilized, which is why I'm wondering if something is interfering with it somehow (third party app?). Did you ever try binding PTT to another key to see how that works?