When you stop the ender dragon respawn sequence while some of the ender crystals have a beam pointing to the center, the beam stays instead of being removed.
- Kill the ender dragon
- Start the respawning sequence
- Wait until at least one of the ender crystals on top of a obsidian pillar has a beam pointing to the center
- Destroy the ender crystals at the portal to stop the sequence
The ender crystal on the obsidian pillar has still a beam pointing to the center