My Sleep | Wake Up Alarm Went Off Silently This AM

I overslept this morning and instantly grabbed my phone when I woke up. The phone was displaying the alarm going off screen with the Snooze and Stop buttons but no sound was coming out. It wasn't counting down a snooze, and it wasn't in the state where an alarm plays quietly when facetime detects you are looking at it. There was no noise at all. I have an iPhone 14 Pro Max on iOS 16.4.1(a). I've been using the same sleep schedule alarm every day since I got the phone a few months ago with no issues. I just tried adjusting my sleep schedule to test the alarm and it went off fine.

Any ideas on how I managed to cause this? It doesn't look like there's a known widespread bug.