"or some other factor like whether you have other alarms at all (even disabled)"

This is the only thing I can think of as a reason why. I have no other active alarms, iPhone 6s.

I think the actual annoying technology part would be that in my half-awake stupor I wasn't able to find that the bedtime alarm moved to the health app without Googling it. As searching "bedtime" in the app search bar still shows the old bedtime app and still launches you into the clock app.