Issue: When alarm goes off, it does not disable the lockscreen and you have to manually unlock the device to tap snooze or dismiss.
Explanation: You may have Sleep as Android enabled under Border lights. This causes the alarm popup to not display over the lockscreen, as the notification is being shown as a light around the edge of the screen.
Solution: Disable Border lights for Sleep as Android in your device’s settings.
On Xiaomi/MIUI, you need to grant special permission to Sleep as Android so that it may unlock your screen during alarm.
Go to System Settings > Permissions > Advanced Permissions > select Sleep app and give it permission to access Lockscreen.