Hey Gatzkerob,
I am on the same mission as you, creating a real time mirror.
In short there is a limitation with Dynamic GI and reflections, it just isn’t quite there yet.
More of an in-depth answer is here.
Basically your best bet is to use standalone Ray trace reflections with Lightmass GI to get the results you want.
I actually didn’t know pathtracer worked with dynamic GI that’s cool. That will be great for stills.
Good luck, I know I am still tinkering with my mirror a bit, but for the most part I have it working with Lightmass and RT reflections. Sucks we can’t use lumen yet for it.