Hi there, I do have a similar issue, noticed it only recently so probably related either to Windows 10 2004 or the newest drivers, 20.7.1 20.7.2 and probably 20.5.1. Haven't noticed that issue before.
It seems FreeSync somehow stop working and the refresh rate stays locked at whatever it was ;
- After long idle on the desktop FreeSync doesn't seems to activate when I start a game ;
- When I leave a game after a long session the resfresh rate doesn't reset to 144hz on desktop and stays locked at whatever it was ;
- After watching a movie for some time on VLC or Edge browser framerate stays stuck at 48hz ;
In all case FreeSync do work again after pressing WIN+CTRL+SHIFT+B
Specs :
R5 3700X
B450 I Aorus Pro Wifi ( lastest BIOS )
RX 5700 XT Reference
16 GB Crucial 3600 CL16