Audio/Video out of Sync on second monitor

So I play World of Warcraft amongst some other games, however the Video and Audio are out of sync with videos I watch on my 2nd screen. This can be either YouTube, Netflix, VLC Player anything but only when playing WOW.

I raised it with them and they replied:

"this sort of issue typically happens when there isn't a enough CPU resources available for the specific core or cores that it is using. If it is using Core 0, like that which wow is using there may not be enough bandwidth available."

Is there anything I can do to fix this issue?

My build is:
CPU - Intel® Core™i7 Six Core Processor i7-8700k (3.7GHz) 12MB Cache
Motherboard - ASUS® ROG MAXIMUS X HERO: ATX, LGA1151, USB 3.1, SATA 6GBs - RGB Ready
RAM - 16GB Corsair VENGEANCE RGB DDR4 3000MHz (2 x 8GB)
GPU - 8GB NVIDIA GEFORCE GTX 1080 - DVI, HDMI, 3x DP - GeForce GTX VR Ready!
1st HD - 1TB SEAGATE FIRECUDA 3.5" SSHD - UP TO 5X FASTER THAN HDD!
1st M.2 SSD - 120GB KINGSTON SSDNow M.2 2280 G2, SATA 6Gb/s (550MB/R, 200MB/W)
Sound Card - ONBOARD 6 CHANNEL (5.1) HIGH DEF AUDIO (AS STANDARD)

If it was just with videos in Chrome I'd have pointed to hardware acceleration.

Have you tried each of fullcreen / borderless fullscreen / windowed modes (for running WoW) to see if it happens in them all?

Are the monitors set to the exact same refresh rate?

So I prefer to play WoW in borderless fullscreen as it's easier to tab out as it keeps the game open in the background.

I always play videos in full screen unless watching YouTube.

Monitors are different monitors. My main is ASUS ROG PG248Q and running with G-SYNC with a DP Cable, the second screen is a 4.5 year old iiyama running at 60hz with a HDMI.

Testing in Fullscreen mode and it seems to be working better and either perfect sync or only just out of sync that you sometimes get with any streaming service.

Is there anything I can do to try and fix this whilst I keep WOW in borderless?

Still having problems after a while on Fullscreen mose

I don't know. I used to tech support MVP for WoW, but it' not an issue I recall, though googling seems to show it is a thing that can happen and be WoW-specific, or that can happen and have nothing to do with WoW.

Try other things like disabling gsync to see if it makes a difference.

If it doesn't, disable gsync and fix the high hz monitor to 120 refresh rate so it's multiple of your 60hz one.

Obviously you wouldn't want to go with that as a permanent "fix" even if it does resolve the issue - but seeing whether this makes a difference could help point you in the right direction.

You could also remove GPU drivers with DDU: http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
and perform a clean reinstall of the latest ones off the Nvidia website.

Another thing you could try is having the 60hz monitor you just watch videos off plugged into the motherboard rather than the GPU output so that it runs off the CPU's graphics. See if that does anything.

So switching my 2nd screen to my Motherboard seems to have resolved the issues. As I'm just watching videos either streaming or VLC Player I might just keep it as that.