I have the following issue I have been experiencing since Driver version 20.11.2 and onward.
When windows power management is set to turn off the display after X amount of minutes and the display turns off after the set time, when the display is woken back up it will default to a much lower resolution of 1280x800 60Hz and no other resolutions are available until the monitor is powered off and then back on at which point it reverts to its correct 3440x1440 144Hz resolution. I was able to revert the driver and the behavior would go back to normal, however I recently upgraded from a 5700Xt to a 6900XT which requires the newer drivers for support and the issue is still present and I do not have the ability to roll back to an earlier driver as the 6900XT is not supported prior to the 20.11.2 driver. I have submitted this as a bug via the bug reporting tool multiple times as well.
The system is fully up to date with all windows updates, drivers, firmware's, etc. yet the issue even persists even after a full wipe and reinstall of the OS, drivers etc. and regardless of which port the monitor is connected to on the card. I have also verified that the DP cable used is a Display-Port certified 1.4 cable and have used this cable on a 2nd system with another 34" 21:9 display (Acer Predator X34) and none of the described issues were present there. (https://www.amazon.com/gp/product/B0767F5DNR/)
These are the specs of my system:
Monitor: LG 34GK950F-B
GPU: PowerColor Red Devil RX 6900 XT (issue was also present with Sapphire Nitro+ RX 5700 XT on drivers 20.11.2 and later)
Motherboard: Gigabyte x570 Aorus Xtreme rev 1.0 BIOS F33a
CPU: Ryzen 9 5950X
RAM: G.SKILL Trident Z Neo Series 32GB (4 x 8GB) DDR4 3600 (F4-3600C14Q-32GTZNB)
Power Supply: Seasonic 1000w Titanium
OS: Windows 10 Pro version 20H2 Build 19042.804
Thanks for linking that thread. Glad to know I am not alone. I tried doing a search on google for the issue, but was not having any relevant results returned.