3 EnderDragon Spawned at once.

I got 3 enderdragon Spawned at once in the ender realm. This is my first time that i got to fight with the enderdragon in my survival world, and i have to fight 3 enderdragon at once this is a major bug and it needs to fix!

To reproduce it
1: play on survival difficulty HARD
2: Find A strong hold
3: Ender the ender realm
To resolve the problem you have to restart the game in the ender realm.