I have to wait until the call stops ringing and then return the call. Started after most recent upgrade installation which was 4/1/19. I have shut down and restarted the phone but that didn't help.
Welcome to Android Central! I've seen some other posts about this kind of issue. I'm guessing it's a Samsung phone that just got updated to Pie, is that right? Are you talking about the incoming call notification at the top of the screen when you're in the middle of using some other app, or are you talking about the fullscreen incoming call screen when the phone was asleep?