Can you try to add:
i915.enable_guc=0
to your syslinux.conf and test if it crashes again, if yes please edit this entry and try:
i915.enable_guc=2
and report back if it's the same.
Have you guys connected a Monitor or a HDMI Dummy plug to your iGPU?
It is much recommended to at least attach a HDMI Dummy plug to avoid Kernel Panics with newer Kernels.
Please don't do this, Intel-GPU-TOP will handle the force probe, just blacklist the i915 module, you even don't need to do a chmod -R 777 /dev/dri because Unraid does this itself if the path is found.