While playing Minecraft with a friend of mine we were just building and I happened upon the structure in the image file below. It was only visible on my screen. I could stand and walk on it, she phased right through it. Any entities (tested with items and mobs) also seemed to phase through it. Clicking on the block with either the left or right mouse button made the blocks disappear. Even stranger was the fact that when I attempted to destroy the block, the block above it also seemed to disappear. Placing blocks on it the the structure placed seemed to replace the target block with the placed block, in stead of it being placed on it. The glitch also continued beneath the surface, and created some overall weird behaviour (as seen in video, on my screen there was no block there, on hers there was).

Note: I was the host and was on windows 10 version, she was on nintendo switch. 

Hope this helps.