I use Google Duo regularly. Lately it has stopped ringing when i get incoming calls, hence i miss many calls...i get an sms sound type when the other person stops the incoming call. If the app is open the phone is ringing. I checked all the possible settings according to Google. Is it a Samsung problem? I used it for years without any issue.
@ZenArcade: Can you try heading to Settings > Apps > Duo > Notifications > Receive 1:1 Calls > Alert (On) > Show As Pop-up (On) > Sound > Default Notification Sound, or choose a custom option. Now, tap the Back button to return to the Duo App Info screen > Force Stop > Storage > Clear Cache. I'd also suggest checking the Google Play Store for any available updates to see if this helps.