FIXED!!

After spending a couple hours on the phone with a very helpful Netflix tech it turns out that MS pushed an updated HEVC Video Extension file, which has broken 4K playback through Edge.

To fix go to your applications. Click start, settings, apps and features, type HEVC in the search box and uninstall the HEVC Video Extension app.

Go to this link: https://www.microsoft.com/en- and install the old version back.