I made it a few hours in on 6.7.9 yesterday after this thread inspired me to check. Still persists and I can now tell if the system is going to hang by starting a video on my second monitor and playing a few minutes of Warframe. The system kind of "stumbles" but won't crash right away. It might even take a few hours to go down, but I know if that happens then the kernel is no good. Happy you got it sorted, though! Lucky for me 6.6 is LTS for a few more years.