MC, regardless of exactly what is going on...report it because even if it is a calc issue or resource usage it still seems like a bug. If you have a bug you have a bug. If you want the render finished you will probably have better luck with a procedural on the infinite plane tho or make it a plane....it doesn't need to be infinite from what I can see. Ialora seemed to have pinned downed the IP as a definite issue so that is the thing to address. Obviously infinite planes work, but there is something else going on with yours. No telling how large the resources are  being used on this.

No need to think outside the box....
    Just make it invisible.