It sounds like you may be missing the <base href=""> tag. This tag tells the Angular router what the base URI is for your application. If this is not present then Angular assumes that the initial navigation URI (in your case, /whatever/someroute/123456) is the base URI and all subsequent routing will be performed relative to that URI.
Try including <base href="https://stackoverflow.com/whatever/"> in the <head> element of your index.html to direct the router accordingly.
You may also control the <base href=""> meta tag via ng build if you are using the Angular CLI:
ng build --base-href "https://stackoverflow.com/whatever/"