I have my Steam, Epic, Origin, and Battle.net integrated to see all my games together, which is brilliant by the way, however I just got Warhammer 40k:Mechanicus on epic and it's showing up as What Remains of Edith Smith on GOG. Not sure what's going on and I personally don't mind but it seems to be a bug.

Possible reason is that it's not available on GOG on it's own?

No, Galaxy knows a lot of games not available on GOG.

Besides that, Mechanicus is available on GOG
https://www.gog.com/en/game/warhammer_40000_mechanicus

Galaxy takes it's info from some non commercial game database, so either there is a invalid entry in that database or Epic provides the wrong game id (which in my opinion is more likely, since Edith Finch gets displayed correctly).

You should report this as a bug, but don't get your hopes up for a fix you might yet live to see.

What you CAN do to make this work: Add Mechanicus manually, mark it as owned. Then set the exe path to the path of your Epic file. You can add the usual "-EpicPortal", in many case Epic games then run without the launcher.


ps: I own the game on both platforms and you are right: The Epic version does not show on GOG version's page.