Hello! There was a problem that I can not solve for a very long time.
It was driver 18.3.4, turned on VSR and gpu scaling, created a custom resolution of 2560x1080 (21: 9) applied in windows and games, everything was displayed normally with black stripes with the correct aspect ratio (first screen).
After that, no drivers work correctly, the aspect ratio does not work anymore, and the image just stretches (screen two).
At the moment, there is a driver 18.9.3, when I create custom resolution, then it is not displayed anywhere with VSR and gpu scaling enabled. When VSR is on and gpu scaling is off, it is displayed everywhere but stretched (screen 2).
With the help of the program Custom Resolution Utility (CRU), the resolution was added to 2560x1080 (21: 9) with VSR turned on and gpu scaling it is displayed everywhere but again stretched (screen two).
My video card Radeon HD 7970 3G, driver 18.9.3, monitor full HD (16: 9) Windows 10 x64 1803
Driver 18.3.4 works correctly (screen one), all later versions do not work (screen two). Help solve the problem. Thank you for attention.
I have a similar problem to yours I'm trying to render games in a lower resolution on my 4k screen to make them playable. I also used cru to make a custom resolution of 3200 * 1800 but It never streches to full screen. I always end up with a native 3200 * 1800 on my 4k screen so with black bars on all 4 sides. I used this without problems on my nvidea card but its not working here. I will try the older driver you said and report back.
As I understand, solutions to this problem will never happen, only one way out: I switch to Nvidia, there are no problems, everything works with any resolution and aspect ratio of custom resolution.