Thanks to randir14 from steam forums I've found out why the steam overlay stopped working, same goes for any other 3rd party tool that has mysteriously stopped working.

You need to delete dxgi.dll and d3d11.dll from \GOG Games\The Witcher 3 Wild Hunt\bin\x64

Last night gog galaxy snuck in a patch that placed these files there.

My question to CD Projekt RED is what are these files for? Were they to fix a graphical issue or for performance? Were they placed there purely to break external tools from working like steam overlay and sweetfx?

D3d11.dll is a file that has the important relation with a program's smooth running on the computer. It is a DLL module belonging to DirectX.

Dxgi.dll is an associated DLL file for d3d11.dll. It is used to support Microsoft DirectX for computer games.

The sweetfx's d3d11.dll I was using worked fine with overlays before the update but after the update it also makes overlays not work like the new d3d11.dll.

Just wondering, for sweetfx do you use the plugin folder?

The sweetfx I am using requires d3d11.dll and told to put all files in the The Witcher 3 Wild Hunt/bin/x64/ folder but in the latest update the d3d11.dll I use got overridden with a different d3d11.dll and I can imagine how it would be a pain to have to keep copying back the needed file after every update haha.

Though, I just managed to figure out that you can use a plugin folder instead so it won't conflict :D

I don't use sweetfx at the moment but have looked at it and might do soon. I primarily wanted the steam overlay.

If there's been two updates one from cd projekt red and sweetfx of the same dll file then maybe its a problem for steam to sort out, support the newer version of the D3d11.dll

What I don't fully understand is if I've removed those 2 .dll files, what does the game use instead, which files does it fall back on?

The files are put there to override the original in windows\system32 , so they have more control. That's how SweetFX and other program work, they completely override DirectX's own file. So they're actually falling back to the ORIGINAL files.

You are aware that this fix was published (not invented, the gog users did that yesterday) in a Sticky Thread in this very Forum 23 hours ago?

http://www.gog.com/forum/the_witcher_3_wild_hunt/streamingvideo_capture_applications_xsplit_obs_sweetfx_etc_currently_not_working_on_some_syste

Sadly it does not work for everyone, dont know why. :)