I went on a world i had created in 2015. I realized that the world border had shrunk and i could even see animals outside the border. I couldn't get to the animals because the border stopped me. Any blocks outside the border were invisible but i knew that they were still there. I turned the world into an infinite world and the problem was fixed and all the blocks were back. I really want this fixed because it looks kinda weird when you turn an old world into an infinite world. I found people make posts about this bug in 2018 so i don't know which versions the bug is in. Edit: I think it happened when the world was converted into a bedrock edition world