Since nothing Microsoft or Xbox people say seems to help on this site or Reddit etc. or even relate to the problem at hand, after messing around I found how to fix this for my situation. Sadly this may turn on more notifications from Microsoft than anybody actually wants....
On Windows 10:
>Mouse Over Bottom Right of the Screen to show 'Action Center'/Notifications
>Click 'All Settings' (Gear Icon)
>Click 'System - display, notifications, power'
>Click 'Notifications & Actions'
>Turn on "Get notifications from apps and other senders" & "Show notifications on lock Screen"
>Scroll Down
>Obviously turn off all the worthless Notifications like 'Cortana'
>Turn on Xbox and whatever else you want.
*Note: Since you said PC in the question portion of the OP I assume that you're looking for a fix for the PC. This seems obvious, but I noticed on other sites people really struggle with the difference between PC and XB1.
Really hope this helps anyone who needs it. I know the frustration of dealing with nonsense.