How can you have missed the call? If it was due to the setting you have mentioned then you will have had to have picked up the phone or looked at it directly for the volume to have been muted/lowered.
Please ask Apple. I did not have such trivial problems on 4S or any other non-Apple smartphone.
Possibly I have not heard a ring because volume was too low.
The problem is that user see that have 80% volume in sound settings.
In my opinion Apple should to turn off "Attention Aware Features" option by default.
How many users who did not have any Face ID iPhone guess that such option might impact ringer volume??! No one!
Now try to imagine that you have an important business call or this was a last call from your parent who is dying due to COVID or your kid was calling because he is in danger. This is unacceptable.
I lowered volume down to replicate a scenario when user watch a video content for example.
With this option turned on ringer volume was too silent. With option off is normal (80% set by default).