Bizarre alarm behaviour

Over the last month or so the morning alarm has increasingly had odd
behaviour.

I use the alarm with the sleep schedule so is always the same time every
weekday, and while it does go off the alarm UI either doesn't appear or is
unresponsive. I'm left with randomly trying to stop the alarm sound by
unlocking/locking the screen until the ui finally appears or the alarm
happens to go off.

I know there's lots if reports of the alarm failing to ring, but this isn't
it.

Anyone else seeing this?

iOS 18.2.1 and normally have the phone in clock mode when charging
overnight.