Board Thread:Bug Reports/@comment-27516710-20160821232722/@comment-27516710-20160822042153

Perhaps another explanation is the lighting errors that come from such large defined generation - similar to the black spots along ravines and overworld villages. These black spots do indeed cause lag spikes and if enough of them exist it could explain the terrible lag (typically small black areas are not a problem, but, if you ever use creative to fly near one in a ravine you'll always get a lag spike as the blocks are updated and the spot vanishes).