Small update, got a reply from amd tech support today, they are gonna investigate, it might take some time... :)
Thank you for the patience.
We have raised an issue report from Engineering level for investigation on this issue. It might take some time as it requires time to test the issue.
As of now, I do not have any solution for this. I request your consent to close this service request.
Thank you for contacting AMD.Got some great news today:
We were able to reproduce the issue and will look to resolve it in a future driver update. There is no ETA for when this update will become available, but you can check the release notes of future driver releases and look at the Resolved Issues section of the driver release notes for additional updates.No ETA but at least it's on their list now. :)
Hey Clubbie,
It's just a driver update, so the solution will be installing the new driver once it's released (and the release notes mention this fix). :P
After the previous email I replied with the MST hubs I tested and the reason why I thought this was driver related, looks like I was right. :)
Part of my email:
I personally think it’s the driver who is limiting the output to one screen per displayport connection.
In the past I had sort of this problem with my Fury X. At first I used the Club3D CSV-5400 to connect four screens to one connection and the other two screens directly to the card. This all worked fine until a driver update (don’t remember which one). After that driver update the card would only see three screens connected to the hub; no matter what I tried. The solution back then was just buying another MST hub and only connect three screens per hub. So I know the driver can limit the amount of screens supported per displayport connection.
Small update, still no fix in the drivers (I hope they make it in the Adrenalin 2020 edition).
But I found out the card supports Displayport MST by playing with Linux (was tinkering with Ubuntu). Four screens on one MST hub are working perfectly. Only problem on Linux is the driver hangs when you turn on more than 4 screens. But at least I now know the hardware supports Displayport MST.