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bug: IonNav.canGoBack() sometimes throws exception: "Cannot read property 'apply' of undefined"

See original GitHub issue

Bug Report

Ionic version:

[x] 4.11.10

Current behavior:

I’m experiencing an exception when using local notifications in an ionic native application. The exception only happens sometimes and I was not able to come up with exact reproduction steps. I wanted to open this bug because maybe someone can help me to point to the right direction so I can come up with exact reproduction steps for this ionic bug.

Basically what happens is that the user receives a notification (while app is in foreground) and then he sends the app to background. After waiting for like 10-30mins he clicks on the notification (while the app is still in background; so not a cold start). By clicking on the notification we check whether we need to pop any existing view before showing the new one with await this.chatRoomNavService.nav.canGoBack(). This produces the following exception: vendor-es2015.js: Line 52957 : ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'apply' of undefined:

Expected behavior:

No exception happens.

Steps to reproduce:

No clear reproduction steps available unfortunately. We were able to reproduce this bug mostly when app got sent to background for about 10-30mins & the phone screen got locked before clicking on the notification.

Related code:

In app.component:
```js
async ngOnInit() {
    await this.platform.ready();
    // Omitted code to simplify example

    this.localNotifications.on('click').subscribe(async (not: ILocalNotification) => {
        // Omitted code to simplify example
        this.chatService.chatInfoOpened.next(false);
    });
}

chat-room-nav.component:

ngOnInit() {
    this.chatService.chatInfoOpened.subscribe(async opened => {
        if (opened) {
            // Omitted code to simplify example
        } else {
            // Omitted code to simplify example
            if (await this.chatRoomNavService.nav.canGoBack()) {
                await this.chatRoomNavService.nav.pop();
            }
        }
    });
}

Other information:

Please note that the examples were significantly simplified so they are understandable.

Linking this issue to https://github.com/ionic-team/ionic/issues/20720 as they are related (both happens in the same scenario)

Ionic info:

Ionic:

   Ionic CLI                     : 6.2.0 (/Users/borntraegermarc/.nvm/versions/node/v12.13.0/lib/node_modules/@ionic/cli)
   Ionic Framework               : @ionic/angular 4.11.10
   @angular-devkit/build-angular : 0.803.23
   @angular-devkit/schematics    : 8.3.23
   @angular/cli                  : 8.3.23
   @ionic/angular-toolkit        : 2.1.2

Cordova:

   Cordova CLI       : 9.0.0 (cordova-lib@9.0.1)
   Cordova Platforms : android 8.1.0
   Cordova Plugins   : cordova-plugin-ionic-keyboard 2.2.0, cordova-plugin-ionic-webview 4.1.3, (and 24 other plugins)

Utility:

   cordova-res : not installed
   native-run  : 0.3.0

System:

   ios-sim : 8.0.2
   NodeJS  : v12.13.0 (/Users/borntraegermarc/.nvm/versions/node/v12.13.0/bin/node)
   npm     : 6.14.2
   OS      : macOS Catalina
   Xcode   : Xcode 10.3 Build version 10G8