Alarm clock turns off on iPhone X

Several times my alarm has not gone off at the time it is set for.

I'm pretty sure it turns itself off if i turn my phone on to check the time sometime during the night.
Is there a setting i haven't noticed that turns the alarm off if the phone is being used?

I have been checking the alarm symbol is showing before i put the phone down each night so it is definitely being set correctly.

(iPhone X)