>They all had problems with very sporadic hard crashes

I had such an issue recently, on a laptop with an Intel igpu and an Nvidia primus card.

I'm not a coward, so I debugged the system, and found that the crash was caused by the Intel i915 driver trying to do some tricky hdmi related mumbo jumbo with the hdmi port that wasn't even connected to the igpu, it was connected to the nvidia gpu.

When I contacted intel bugtracker, they just said "ah, Nvidia... well, even though their kernel module is open, it's not on the mainline kernel, so go fsck.ext2fs yourself".

I have also seen extremely rare cases of Linux freezes exactly like you described, and I have wondered if there can be any relationship between them and the NVIDIA drivers, mainly because they are the only closed-source drivers that I use.

Nonetheless, I have not seen any evidence about such a relationship. The freezes never occurred while the computer works alone and some program uses the GPU. In all cases the freezes happened right after some quick mouse movement.

The culprit is definitely somewhere in the device drivers, and it cannot be excluded that this may have something to do with NVIDIA, because I do not remember if I have ever seen identical freezes with AMD or Intel GPUs, but that could be just because I have spent less time using directly such computers, instead of using them remotely through SSH.

In any case, this bug is something that requires interactions with the mouse driver, perhaps also with the keyboard driver, and the X server might also have some role.

In such cases, network and HDD/SSD activities appeared to continue normally, only the display was frozen and the keyboard and mouse did not respond. While the initiator could have been something done by the X server, something was stuck in the kernel, because not even the keys that should be intercepted by the kernel worked, as you have also said.

This is certainly a bug whose cause has not be discovered for many years, but it is not yet clear whether it really has anything to do with NVIDIA, since its main effects are upon keyboard and mouse.