Sorry, there are multiple issues rolled into one post so this might be long...
So I have an RX6900 XT and am using it with a Dell S3221QS over DisplayPort. I also have a Samsung U28D590 hooked up over DisplayPort. The Dell is my main monitor and I use it for gaming. It is supposed to support Freesync from 40-60 Hz. That's from both the Dell website and what the monitor reports to the AMD drivers. The Samsung is not freesync and supports 60Hz. Both displays are 4k.
I've been playing Diablo 3 for years with no problems (previously GTX1070) but after switching to the 6900 in the last couple weeks I started getting headaches and nausea. I realised that there is now subtle, high speed brightness flickering in the game. It's most noticeable in dark areas but it's there most *(see below) of the time.
This coincided with me switching to the 6900 and turning on Anti-aliasing. I've done a bunch of testing with different game and driver settings working to resolve the flickering and in the course of this I've noticed more problems.
If I turn OFF anti-alising I don't get the flickering (irrespective of Freesync setting).
If I turn OFF Freesync I don't get the flickering (irrespective of AA setting).
So, essentially, if I enable anti-aliasing with freesync on I get flickering. Which is bad enough to literally make me sick.
Now if I turn on the Radeon Metrics overlay I don't get the flickering even if I have both FS and AA on. Which begs the first question; does turning on the Radeon Metrics overlay turn OFF freesync?
Second question: Why is there this terrible flickering when using FS and AA?
I thought this might be related to the framerate going outside what the monitor can display. This seems possible since the Dell has such a narrow FS range (40-60 Hz). Since D3 has an option to cap the Max FPS I tried setting that to 60. This had two effects, first it got rid of the flicker. Second, it dropped the actual framerate to 32 FPS.
Again, this looks as though Freesync is not actually running. Surely a freesync monitor with freesync enabled in the driver should display at 60 fps? I wouldn't expect it to hit 32 fps unless the framerate drops below the minimum of the freesync range (40 Hz). Incidentally this framerate drop occurs regardless of whether freesync is on or off in the drivers. So is freesync just not working at all?
It's not like the card cannot produce enough FPS either. With max graphics settings and 8xAA if I set the max FPS to 200 (the highest setting) the framerate sits at about 165 FPS though it fluctuates by 20ish fps. Setting the Max FPS to anything from 65 - 133 gives me a steady 65 FPS. 64 and below immediately drops it 32 FPS. 134-153 the FPS sits between 65-70. If I put the Max FPS over 153 the actual framerate goes up in proportion to the Max FPS but fluctuates by 20 FPS (just like when Max is at 200 FPS).
So again, is Freesync just not working? If it's not then how can I tell where the problem lies ie: monitor, video card, drivers, game, windows?
And how do I use the card with Freesync and AA without getting this horrible flickering?
* The weird thing about it is that the flickering happens most of the time but not all. For example, it's been happening every time I've got into the game all week (literally more than a dozen times). But it's not happening today, no matter what settings I choose.