Ionic app accidently closed by hardware back button

I am using fcm push notification. After click on notification (when app is in background), i did route to component inside platform ready. After route, when i pressed the hardware back button instead of going to previous page, it accidently closes the app (ion back button worked properly here).
Also hardware back button not listening to any related events like this.platform.backButton.subscribeWithPriority(). Need the assistance as it is the major bug and crashes the app. If there is alternative to navigate fcm push notification, please suggest.

This is my configuration -

Ionic CLI                     : 6.12.1 
Ionic Framework               : @ionic/angular 5.2.3
@angular-devkit/build-angular : 0.901.11
@angular-devkit/schematics    : 9.1.11
@angular/cli                  : 9.1.11
@ionic/angular-toolkit        : 2.2.0