I got similar issues and seems it is related to some kind of rubbish code between outlet and back button validation that Ionic do inside, I'm not sure what the problem is, but from my side, to save my time, I just removed this useless component and did re-write my own back button. You can look at my answer in the forum here: https://forum.ionicframework.com/t/ionic-4-back-button-angular/137866/25