This doesn't affect the host.  I play on a multiplayer world on LAN, and occasionally when I place blocks the blocks don't exist on the other player's screens and technically don't exist, as if I place a block the amount of that block in my inventory remains the same, meaning that I never removed that block from my inventory by any means. Whenever I mine the non-existent block it doesn't drop. however, I still see the block and can interact with it. 

In the video, you can see that I place the blocks but the amount in my inventory are the same, and when I mine them they don't drop. Also, my friend can walk through them because they don't exist on his screen.  

 The no-existent block will disappear if you rejoin the game, but the glitch does not.  If I try to rejoin to fix the glitch, I will continue to place non-existent blocks. Restarting minecraft isn't very fun to do, so I hope my complaint will help solve this glitch. Thanks for reading my feedback, and have a great day!