Hello, since Windows 10's Creators Update and beyond when having multiple monitors (even one with high resolution and refresh rate, i'll explain), everytime i'm opening an UWP app (affects every UWP apps), the cursor / system (except sound) will freeze for like a second, and this little freezes happen also when you open new tabs in Microsoft Edge but also occurs when doing specific things like opening the "Display" tab of the System category in Windows Settings, but this DOES affects win32 programs too, when clicking on the switch screens button on ultramon (wich is win32) it also causes this little freeze.
The issue can be observed in his worst state when doing the specifics (haven't found other ways yet) (The monitor setup i use is: BenQ GL2250, Asus MG278Q, AOC e2343F2, it's very important i'll explain why):
-Opening Minecraft using MultiMC with Forge + Optifine (using lwjgl 2.9.1), all those steps are very important in order to make the issue occur, then when the game will start, at the precise line "*** REFLECTOR VANILLA ***" the whole system will begin to lag, on Anniversary Update, the system would lag for only 6 seconds, slowing down the whole system to 30 fps till the game opens up, the freeze will stop.
On creators update and beyond, i would get a total of 2 MINUTES and 20 seconds of lag while the system is slowed down to 1 fps
Opening GTA SA (requires more than one screen to bring the screen selector box and trigger the issue) also trigger the issue.
Now, when i unplug my MG278Q, those issue will be WAY less important letting UWP apps free of freezes, but still not when opening the games above, if i unplug one of the 1080p monitor, it will be better, not by a lot but it will still be an improvement.
It seems that the biggest resolution and refresh rate (+ freesync or g sync technology) is, the bigger the freezes will get, as the MG278Q itself makes 20x more freezes than two 1080p monitors.
Setting the MG278Q to a lower refresh rate and resolution doesn't help.
If i plug the screens to other PC i will get the same results.
Using Intel igpu or Nvidia GPU also suffers from this issue but seems to be way less affected by it. (used Surface Pro iGPU and GTX 670 for testing)
Same freezes happens on linux, on Fedora it freezes when opening programs just like Windows 10 Creators Update, on Ubuntu it's less consequent and it will just lag when opening Minecraft and GTA San Andreas.
Here's a link of some users reporting the same issue
With the minecraft case, using LWJGL 2.9.4 actually makes the game free of this freeze issue, i don't know what the dev changed to make the freezes stop, but here's how to upgrade to lwjgl 2.9.4 on multi mc: Modify Instance > LWJGL > Personalized > Modify and paste https://pastebin.com/4d3HH5FF and the lags completly disappeared for Minecraft.
Default launcher of minecraft is using LWJGL 2.9.4 by default.
I noticed when doing an Eyefinity setup the lags will be also less consequent.
Also tried to swap my Vega for a 280X and the freezes are the same.
I tried my best explaining the issue as english is not my native language, so for the moment i'm staying on Windows 10 Anniversary Update to prevent the freezes everytime i'm opening an app as it's extremely annoying.
Windows 10 Fall Creators Update
AMD R7 1700
AMD RX Vega 64
16 GB DDR4
Asus PRIME X370 PRO
BenQ GL2250, Asus MG278Q, AOC e2343F2
tl dr: Having a "big" screen with high resolution and refresh rate with g/f sync technology makes the whole system stutter when opening apps since Creators Update and beyond, plugging more screens makes it even worst, happens on Linux too, and even on intel and nvidia gpu but they are way less affected by it.