router navigate with relativeTo parameter can only success once

# Bug Report
**Ionic version:**

[x] **4.x**

**Current behavior:**

navigate to next page failed!
router navigate with 'relativeTo' parameters will only success once, after back, you can never enter target page you want.
**Expected behavior:**

should navigate to next page back and forth successfully everytime

**Steps to reproduce:**
**Related code:**

open a blank ionic project,
use codes below will navigate to next page successfully only ONCE, after click back, you can never enter again.
In success round, variable ret returned True. In failed round, ret is null. whereas open a blank raw Angular project, everything is running correctly. Only Ionic failed.
```
let ret = await this.router.navigate(["../test1page"], { relativeTo: this.route });
console.log("ret=", ret);
```

**Other information:**

Using a blank raw Angular 7 project, router is running correctly at the same condition!!!

**Ionic info:**

Ionic:

ionic (Ionic CLI) : 4.10.3 (/Users/avex/temp/ionic/node_modules/ionic)
Ionic Framework : @ionic/angular 4.0.2
@angular-devkit/build-angular : 0.12.4
@angular-devkit/schematics : 7.2.4
@angular/cli : 7.2.4
@ionic/angular-toolkit : 1.4.0

System:

NodeJS : v10.13.0 (/usr/local/bin/node)
npm : 6.8.0
OS : macOS High Sierra
```
insert the output from ionic info here
```

Start with a blank Ionic 4 project and reproduce the router.navigate call using '../test1page' and relativeTo: this.route, then compare it with the reported working Angular 7 project. Confirm that navigation still succeeds after going back and entering the target page repeatedly; the issue provides no source file or test location to inspect.

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