Ok, thanks again, I’m now fixing it with blueprint, on the menu map. I execute command to leave fullscreen as a blueprint “onBegin”. Seems good. But I don’t find it clean. As an example, when I create a new genericshooter project (without steam or anything) on 4.13, same issue is happening (while there was no migration or stuff added, and genericshooter is up to date). I think the issue is deeper, and I don’t really like these kind of fix. Oh, and btw, if I run the game in the editor as standalone, it’s perfect. Fullscreen, resolution fitting the windows settings, and everything is good. I don’t know what’s happening but this little fix should work for some time.
In the end it’s an issue about how genericshooter deal with player resolution when enabling fullscreen at launch (I think there’s something with dualscreen as well)… I’ll let all you know more if I get more informations.