So, when I just started using GOG Galaxy 2.0 everything imported fine and all my installed games were detected perfectly. And it was working great for weeks, now it seems to have lost swathes of my installed games. They are still in library, but marked as not installed.

I've tried refreshing the plugins, restarts, running as admin and nothing seems to fix it. 29 of my 110 installed games are still shown. The rest are not. When I click Install on the game page, GOG says "please hold on, we are launching a steam game" but the game never launches, nor does it try to reinstall or anything like that.

I'm posting this here for a quicker response, but I'll also be sure to make a bug report.

I've had the same problem for a couple days, and just now tried to seriously solve it.

For me, I discovered that Steam just got disconnected from GOG Galaxy. Since all the Steam games were still in my Galaxy library, there wasn't any real indication of that happening - no error message, no "would you like to connect again?" dialog, etc..

It was weird, because the plugin was still listed as connected and running. And some Steam games were there but not all. But yes after reading this post I just disconnected it and reconnected, that seems to have fixed it.

Well, in this case try to reinstall the game without downloading this helped many users to fix the Steam fails in recognizing the installed games.

Also if you are having game data in the Steam apps folder, then you would force Steam to detect the games by starting the game installation problem.

• First, start Steam > go to Games.
• Now choose & click > install for the games that Steam failed to identify.
• And after installing the steam world start determining the existing game files.

Hope this works for you to fix the problem. But if not then try the other solutions like Manually Add Steam Library Folder or check the game integrity of through steam.

Source: http://www.pcerror-fix.com/fix-steam-not-recognizing-installed-games