No new gateway spawned when a enderdragon was killed.

What I expected to happen was that a gateway would spawn after I killed a new dragon on a server (for Patreon members).

What actually happened was no gateway spawned.

Steps to Reproduce:
1. Spawn an enderdragon. It did not work when I just placed the normal end crystals but someone else managed to get a dragon to spawn.
2. Kill the dragon.
3. No new gateway spawns.