There is an issue in the latest builds when rendering with Embree ON - if you run out of memory parts of the scene don’t render at all. Could you check if you have enough memory to render the 6k ? You can also try turning Embree OFF - then you will most probably get errors.
If you have 3D displacement, increase its edge length and then you should be able to render with Embree. Or otherwise increase the size of your swap file and it should work too.