New S21 Ultra and I have the DND set between 9pm and 8am but despite this notifications are still happening.
My phone is on vibrate most of the time, but I do not see why that should affect matters.
Running Android 12
I have to keep manually turning it on.
I have removed the setting and recreated it.
I do have favourite people can call me only.
Just happened to me too last night. To make matters worse it was Monday morning, worst day of the week! I have turned all notifications off because I could take it happening again.