Through trial and tribulation, I figured out why AutoWake malfunctions at times. My first guess was that problems occur if the alarm is set after my iPhone goes into sleep mode at 10pm. A test demonstrated that was not the case. (An alarm set at Thursday 9:47pm for Friday 6:47am did not go off; the iPhone app showed it was set for Sat 6:47am.)
Soon, I became suspicious of the iOS app. Tests on Tuesday, Wednesday, and Thursday proved it really was the culprit. If I set the alarm on my watch and open the AutoWake app on my iPhone, then the alarm becomes misconfigured and won’t sound.
All its bugs (i.e. the one mentioned above) and flaws (i.e. chugging tons of battery) make me wary about using AutoWake, but I’m going to stick with it for now. Maybe it’s all in my mind, but waking up in light sleep while having such an adjustable alarm sure does feel nice. You may call it a petty luxury, but I already paid for it so might as well get my money’s worth.