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.
Linked issues
duplicates 1
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The teleport backwards is just latency to the server
Horse taking fall damage all at once is a duplicate of MC-147889
This may be related to MC-147772.