If you lag the server, when you go through an end portal, it doesn't save the actions of the chunks near where the gateway is located, and this allows you to duplicate items or get some black states that aren't intended, like a floating torch.

This makes some situations like the shown in the following video: https://youtu.be/Wi1rLkM2D1g

This is my first bug report, if something is wrong or needs to be  changed, please tell me.