jorimt wrote:If you haven't already, you can attempt to disable Windows game bar and/or "fullscreen optimizations" for the game's exe, which will, in turn, disable Window 10's exclusive fullscreen/borderless-windowed hybrid mode. If that doesn't work, it's down to that specific OS update's interaction with the driver, and you'll have to wait until it's fixed by one or both sides (Microsoft/Nvidia).
Some have also reported the G-SYNC borderless/windowed mode isn't working properly (hitching) on the latest consumer version of Windows 10 (1709).
Since the G-SYNC borderless/windowed mode relies on the OS's DWM to function, this is pretty much an unavoidable issue for problem driver/OS updates.
I tried disabling "fullscreen optimizations", which didn't make a difference.
I did notice however, that after DDU'ing and installing an older (or the newest, didn't matter) driver, gsync windowed worked for as long as I did not reboot my computer after the driver install. After rebooting, it was broken again.
This led me to believe that something goes wrong in the startup, whilst initializing DWM. I disabled fast startup, but that didn't help. What does (temporarily) remedy the situation though, is
manually killing dwm.exe. It restarts, and every game I start then has working windowed g-sync.