While playing singleplayer on a hardcore world I was riding on my horse and occasionally got teleported backwards. I thought it was kinda annoying, however "no biggie". After this had happened 6-8 times it happened once more. Once the game had caught up and teleported me back I was instantly dead. The cause of death according to the game being "fall damage" yet I was on a flat surface with full health, and so was my horse with full diamond horse armor and 14 full hearts. Not sure why this happened, but it's clearly unintentional and undesireable.

I then went into spectator mode to see if I could figure out what was going on and as seen in the 2nd picture (named Screenshot_112) the world simply disappeared and won't load no matter how long I wait.