Dragon Health Bar doesn't appear

Summary
i went to the end and the ender dragon had no health bar

What i expected to happen.
1) Visit The end
2) Destroy the end crystals
3) Fight The enderdragon while being able to see his health

What actually happened
1) I visited the end
2) Destroyed the towers
3) went to kill the dragon
4) Didn't see his health bar

Steps to reproduce:
1) Go to end dimension
2) Destroy end crystals (Or Respawn dragon and destroy end crystals)
3) Attack dragon
4) Health Bar doesn't appear