Invisible blocks on edges of world

Almost two weeks ago a large portion of blocks near all the borders of one of my worlds suddenly turned invisible. I can still walk in the invisible portions and even can break the blocks there, except on one side I can't enter the invisible part. I made copies of the world in case things got worse and in one of them I got trapped inside a block (2nd video). Most recently, if I try to walk into the invisible part on that one side I get stuck there and the world starts glitching. My iPad mini is only a few months old with 128gb of space so I don't think my device could be the problem...
(App store says Minecraft version is 1.2.16)

Screen videos:
https://youtu.be/2vcebx6qaRg

https://youtu.be/fsQ4xoIbONc