I am not sure what wakes me up, I just do and can't get back to sleep unless I take it off. My insomnia is rather strong. I do find similar to you that the machine decides it's time to exhale before my natural breathing wants to exhale. It's like it starts to suck the air out of my lungs. What you call "dropping out before done exhaling". The inhale seems a bit too much as air can go into my mouth/stomach which is irritating and also affects my wakefulness. Some setting to increase the time length of inhalation was increased to max, which helped a lot, but it still does it unless I take a large, faster breath - which is, of course, not natural. The min and max numbers were also adjusted but I don't remember what they are. Will call (yet again lol).