You could try a couple of things to find out which app created this alarm.
- Not an easy one, you need to stay awake just before the alarm goes off About 5-10 minutes before the alarm time you get an 'upcoming alarm' notification. Swipe down from the status bar, long press on it and tap on 'app info' to be sure which one is sending it.
- Access your notification log and scroll down the list until you find the alarm. In some devices you need a custom launcher to create a widget to access this log. Long press on the screen, tap on 'widgets', scroll down until you find settings, drag it to the screen and select 'notification log'. If your stock launcher doesn't include this option you could try with Nova or some notifications manager from the Play Store.
Another thought. What happens if you tap or long press on different places inside the clock widget? Do you get any extra info specially if you tap on the alarm?
That's weird. Any alarm should register in the notification log after its triggered. Not sure what else to suggest. Just a question. That clock widget with the app shortcuts, is it stock or from a third party app?
The screenshot shows Bluetooth enabled, are you using a watch or a similar device? If so, can this paired device manage alarms on its own?