Visible Blocks on flatland suddenly disappear

I opened my Minecraft and turned on my custom resource pack (currently unreleased). On my test flatland, I found that suddenly the grass blocks ended quite close to my player, like buggy fog, although I could not affect it with my render distance or fog settings. Blocks above the grass appeared visible, although beyond the point where they cut off the colours were heavily distorted. In the screenshot example, you see a village. Although it is midday, the village appears black, apart from the crops which look purple. The area after where the blocks cut off appears to be the void. A hole shown in the screen shot (From a wither) meets the point where the grass cuts off and shows a similar distortion effect.