In certain circumstances, entering a nether portal in the end would teleport the player to somewhere around the 16-bit integer limit on the y-axis above world spawn. If the player reaches the ground without dying, the entire world is (mostly) unable to be interacted with. Blocks cannot be edited, mobs cannot be spawned or killed (mobs that existed before would still be able to move), items cannot be dropped, block entities cannot be placed, but projectile items (such as potions and snowballs) can be thrown, though they appear to teleport somewhere near spawn. Reloggining teleports you to about 100 blocks above spawn and reverses most of the effects of this bug..

Here’s a hastily made video about this https://youtu.be/Uj8-9w1F_yE