RNG

Here you are going to find information about Random Number Generation aka. RNG particularly in Minecraft.

RNG in General

Mathew Boland has a nice series explaining this using minecraft seeds: Seed Finding and Reverse Engineering

Entity RNG

Servers and RNG

TL;DR: Entity RNG manipulation(the manipulation done in this mod) doesn't follow the default behavior on some servers and thus some features of this mod don't work on servers with the brands named in Servers, that beak the default RNG behavior

There are many different server brands, which all have some modification to the minecraft code. Some try to be more optimized, and change with that some default behavior in minecraft, like RNG. As long as it doesn't say one of the servers listed in Servers, that beak the default RNG behavior everything to do with RNG manipulation in this mod(for ex. /cenchant) should work fine.

Servers, that beak the default RNG behavior:

• Paper

What is my server brand?

Press f3 in order to open the debug screen.
In the 3rd row on the left your server brand should appear. By default in single player it should say integrated server.