Try a soft reboot by turning the phone off and on.
If no help then put the phone in Safe Mode which disables any downloaded apps and leaves the stock ones Live and then see if you show missed calls.
If you do then one or more of your apps is causing the issue.
In the past apps such as true caller caused conflict.
Also try turning call Caller ID and Spam Protection.
Launch your phone app and press the 3 little dots in the top right hand corner.
samsung-galaxy-s9-s9-plus/874907-no-missed-calls-notifcation-s9.
Daily Driver > Samsung Galaxy s²⁴ Ultra 512Gb ~ Titanium Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
