What all could be the reasons for a NavigationCancel event to get triggered?

NavigationCancel will be triggered when you are trying to naviggate to a route and navigated route children can not be loaded (CanLoad guard) or route itself cannot be activated (CanActivate guard)

you may use {enableTracing : true} while configuring RouterModule to see all events, and analyze further.

Hope this helps!!

This is late, but i hope it might help someone else, as I had struggled with this also.

So, another reason this could be happening is that the navigation event is triggered twice.

This happened to me by mistake, because i had a component with a routerLink directive that had an input binding with the same name:

my-component Class:

@Input() routerLink: string[];

my-component Template:

...
<a [routerLink]="routerLink">
...

The parent component template was like this :

...
<my-component
   [routerLink]="somePath"
   ...
>

Which was actually creating another routerLink directive binding. As a result the navigation event was firing twice, almost simultaneously, which produced the NavigationCancel event.