Hello there ,
I have the exact same problem. Played for like 60h in act 1and had 90 fps at 4K ultra settings until i arrived to Grymforge.
Now i just can't continue playing the game because it crashes after 5-10 min or so.
My setup:
R7 5800 X3D
RX7900XT
32go ram
WIN 10 64b
Amd drivers are not up to date for BG3 and i hope they do it quickly, also waiting for Larian news concerning the next patch/hotfixes.
It's quite frustrating to be locked in an early access state (not being able to go further i mean).
