Dear Mojang Team,
I know that this issue is possibly a duplicate, but when 1.9 was released today, I went to my 1.8 world and it said it was now a 1.9 world, but the world was like, crazy, and the blocks were changing everywhere every 2 seconds. Usually I lower my render distance to fix this issue but I lowered it down all the way this time and this render distance issue has now completely destroyed my world. Sorry if this is a duplicate and wasted your time!