Navigate after modal closed is not working properly.

[Guervyl]

Describe the bug
When I open a modal and navigate to another page in the modal callback/promise, the page opens and then open the page that was opened before and multiply the pages in the stack. My solution is to wait for 300 milliseconds to navigate to the other page. This solution works with no problem. But my concern is if on some other devices the modal take more time than the 300 milliseconds to navigate back y application will break.

To Reproduce
Navigate to a page and open a modal in that page. Navigate to another page as soon as the then promise is called.

this.modalService.showModal(MyModalComponent, {
    fullscreen: false,
    viewContainerRef: this.viewContainer
}).then(ajoute => {
   //router is RouterExtensions
    this.router.navigate(["/a-page"], {transition: {name: 'slide'}})
})

Expected behavior
The navigation should works with no problem. The promise was supposed to get called after the modal navigate to the page it was before.