Just came back to this thread to say that there's something weird with this board. I tried updating the BIOS out of curiosity to the first one released with Windows 11 support (BIOS 3601 to 3701). As soon as I did this, the short stuttering/freeze issue came back, so I reverted to 3601 again and everything seems fine again. I know it was also doing it with the newest one (3801).
I'm wondering what has been changed/added in those BIOS versions that would cause this kind of trouble. Not that I would like to update to Windows 11 right now but if I need to in the future, I'd like to be able to.