Gears of war 4 has been removed from my Library

A while ago when Gears 5 was being launched, Games with Gold had Gears 4 as one of the "Free Games" offered. I purchased the service downloaded the game and played. Later when my hard drive was full, I had to sacrifice Gears 4 for space reasons. Recently
I discovered that Gears of War 4 was missing from my library! I have it showing in another service (GOG Galaxy) but it's nowhere in my Xbox services, no record, nothing!! I rejoined because of the Gears 4 "free game" games with gold service. I'm miffed and
want to know what happened to it!! Please, if anyone can explain or help me I would be grateful.

:)