When entering a world, the sides of nearly all block textures are broken, Grey and Black stripe, upon loading world. They are fixed when a block near it is updated. They can then break again when a Trap Door of any kind is opened / closed. I found this in Minecraft Bedrock Ed, beta 1.12.0.2

Images attached shows this glitch in action, this is meant to be Iron Blocks and it shows the small stats at the top of the screen. I posted this on the Minecraft Feedback page under MessyDiamond2.