It took me a while to get this one, because I don't usually have root urls that need matrix params. An app with such urls:
https://someurl.com/;page=1;category=mice
That won't work, they must turn into query params
https://someurl.com?page=1&category=mice
W3C says so
It is only sensible for relative URls which start with ";" to take a set of attribute values which are different from those of the base URL.
So in Angular, you have to watch queryParamMap instead.