I once had a problem with a new Xiaomi phone where the OS would put the clock app to sleep and the prevent it's background activity, missed 3 alarms before figuring it out.
I had the same issue, but i was using a third party app because i don't really like the default one and a year later the problem started, now i am forced to use the default app if i don't wanna my boss waking me up again
Never had this issue when I had an iPhone. I was super annoyed by the snooze button being so big, though. Made me think I phone users must be lazy as shit. Who needs a snooze button that's bigger than the "dismiss alarm" button?