Got mode has simply no effect. Typing the command "/god" it says "Invincibility activated" but monsters still do damage to myself. Typing "/god" again supposedly deactivates it again but again with no visible effect.

Running Spigot 1.10.2 (exact version: git-Spigot-a9631d2-67b2424 (MC: 1.10.2) (Implementing API version 1.10.2-R0.1-SNAPSHOT))
and EssentialsX 2.0.1-b368

Startup Log: http://pastebin.com/9xCvj680

Also noticed that /afk will not make the player invincible either, even though I set it in the config that they should be.

Uh are you sure you don't have any plugins interfering? Try reproducing this with just essentialsx installed.

Problem was caused my another plugin named RandomTP. Without it everything works just fine.