Flat World is no longer infinite and full of holes

Building map in flat world for a while. Now the map is rendering with holes/voids. There are some area were I had placed blocks but it is now displayed as void. I can see the wire frames showing where those block are. Not much of the map I was working on was damaged, but I don't want to continue until this is figured out.

What was an infinite map is now met with voids at points N,S E and W. Edges are rough the map does not turn to void at the same N , S, E, and W coordinates.

Not able to produce screen shot ( perhaps I need to open an issue for that as well.)