Do you have VSR enabled and GPU scaling enabled?
Have you set the display scaling in the application or game you are having this issue with?
The supported resolution for VSR:
Target Display Timing Supported VSR Modes 1366 X 768 @ 60Hz 1600 X 900
1920 X 1080
1600 X 900 @ 60Hz 1920 X 1080 1920 X 1080 @ 60Hz 2560 X 1440
3200 X 1800
3840 X 2160 (AMD Radeon™ R9 285, AMD Radeon™ R9 Fury Series)
1920 X 1200 @ 60Hz 2048 X 1536
2560 X 1600
3840 X 2400 (AMD Radeon™ R9 285, AMD Radeon™ R9 Fury Series)
2560 X 1440 @ 60Hz 3200 X 1800
I wrote "Preserve aspect ratio etc" - does not give anything.
All the same, the picture is stretched.On the driver 17.7.1 there are no problems with a resolution of 21:9 (2560x1080, 3200x1080, 3200x1100, etc.) on the usual FullHD16:9 monitor.
I am well versed in the components, etc. All the banal tips have already tried.
On the old driver it was possible to disable EDID, I think this is the reason.
At 21: 9 resolution, there should be black bars at the top and bottom to maintain the aspect ratio, but in the new driver 17.7.2 they do not exist and the picture is stretched to the full screen.
On the driver 17.7.1 and older, everything works fine.
This is the video that I made for my channel.--> How to put the resolution of 21: 9 on a normal FullHD monitor? - YouTube
It is in Russian, but there I explained how to use VSR and the registry to set a non-standard resolution. And it's perfect work on my TV and the old drivers. But on the driver version 17.7.2 the picture became stretched, and I do not understand why, the guesses I described above.
Sorry for english.