I just subbed to Ubi+ membership, and I tested Valhalla out and it seems to work just fine. When I try to boot up AC:Mirage it just shows an Ubisoft window that it is "initializing..." and for a split-second the window dissappears.
After that I had to stare at the GFN background for an couple seconds just to bring me back at the main-menu. I have experienced this before with AC:Rogue.
Is there any solution to this?