I'm happy to report 5+ days of uptime with no issues.
After months of debugging, I finally found that the issue was related to a combination of two factors: buggy Nvidia drivers and bad AVX offset (I detail this matter in a previous post on this thread).
Any old Nvidia drivers prior to the latest 387.10.10.10.30.106 were not correctly supporting my Nvidia Titan X Maxwell:
As a result, every 2-4 days the driver would randomly panic, leading to the CPU stuck in a loop with AVX instructions and the screen frozen. And because my AVX offset was incorrectly set that loop was triggering a Kernel Panic before the Nvidia Driver issue could generate a bug report to the system logs. Visually it was seen as a hard freeze with no auto reboot, and no SSH connection possible to the machine. The only system log available was the Kernel Panic that would state that something happened (cf my previous posts)…
After adjusting the AVX offset to a proper value, I would still get these random freezes (which were no hard freezes, as the system would be able to recover), the Kernel would be able to restart the Nvidia Drivers. Visually, what would happen is that for ~20 sec there would be a high CPU load just like before. After ~20 sec the screen would turn black and restart WindowServer, so bringing me back to the login screen and effectively killing my session including all running apps. Also the Nvidia drivers would generate a bug report in the system logs! Finally, giving me a clue about what was going on.
When the 387.10.10.10.30.106 got released, big relief… no more random crashes. The issue was gone, and I can now fully enjoy my hackintosh.
What helped me debug this issue was Fortnite. This game was somehow able to trigger the exact same random freeze that I was getting at random occasions (every 2-4 days of uptime). This is what helped diagnose the issue faster and how I discovered the AVX offsets were part of the equation! The latest Nvidia drivers are still a little bit buggy (i.e. getting a few crashes from time to time with Fortnite), but at least I don't get random freezes.
For those out there who try to debug their issues, the best is to make sure not to have any Overclocking-enabled and make sure that your system is stable on Windows and Linux. I could have avoided months of debug if I had left all my OC settings as default (with the default AVX offset settings)... Although that wouldn’t have solved the buggy Nvidia drivers but that would have given me a clue about what was really going on.
Good luck!