When connecting a second display to my computer my BenQ XL2730Z exhibits some strange behavior. Two things happen...
One is random display corruption (https://imgur.com/a/pzyvSB8) and the other is the screen going black for a few seconds and the returning to normal.
This only happens when a second display is connected to my PC and only happens when connected via DisplayPort (I haven't seen it happen via HDMI).
I have tried a bunch of different driver versions and they all exhibit the same issues.
I have swapped out the Display Port cables to make sure they weren't faulty (tried two I had on hand and purchased two brand new ones as well).
I tried swapping the ports on the back of the GPU and the BenQ display still has issues regardless of what DP is used (The second monitor doesn't show any issues).
I have also tried running other monitors in a dual monitor setup and none of them have issues (none are high res, high refresh rate or support Freesync like the BenQ does).
Now here is where things start to get confusing...
The problem doesn't seem to happen if I use a different model of video card.
I had a reference Vega 56 GPU and when I replaced it with my spare RX 460 the problems went away.
Thinking it was a GPU problem I had the Vega 56 RMA'ed. During the month the card was away I ran the RX 460 and didn't have any problems using multiple displays (that I saw).
The card was replaced with a Nitro+ Vega 56 and upon reinstalling this new GPU the problems started happening again.
I have just had the BenQ monitor serviced at looked at, and the technicians couldn't find a fault with the display or even recreate the issue (but they didn't have any Vega cards to test with, and from my testing the fault only happens with a Vega card).
This brings the fault back to being a GPU issue (or perhaps a compatibility one).
I'm completely out of ideas on how to solve this problem (without spending an arm and a leg replacing either the display or the GPU) so I was hoping someone here might be able to help?