Setting to show incoming call-screen to answer
Usually when you have an app running, and a call comes in, You hear the ring just fine, but cannot find option to answer the call and it often shows up as missed call. Also If you don't have another app running, then you might see the incoming call-screen just fine.
Solution: Make sure that in Settings> Apps>All>Dialer, see if Show Notification is checked. Let us know how it works by adding your comments in comment section.
Usually when you have an app running, and a call comes in, You hear the ring just fine, but cannot find option to answer the call and it often shows up as missed call. Also If you don't have another app running, then you might see the incoming call-screen just fine.
Solution: Make sure that in Settings> Apps>All>Dialer, see if Show Notification is checked. Let us know how it works by adding your comments in comment section.