a few months ago, I had a similar issue with P6, also a multi figure image, with background etc... it was rendering right up untill the bottom right hand corner, and stopping and leaving a grey blocky area.... Im not 100% on this this, but I have a feeling it may have something to do with memory.

Perhaps save the project, then start removing small props and items from the scene, and doing small quick renders to see if this solves the problem....

"If toast
always lands butter-side down, and cats always land on their feet, what
happens if you strap toast on the back of a cat and drop it?"

Steven Wright