Ender dragon consists of 9 entities in total

The bug

This happen since 19w08a.

When summoning an ender dragon with /summon command or spawned in end it will spawn 9 times all fixed to one.

How to reproduce

Spawn an ender dragon

/summon minecraft:ender_dragon 

Kill the ender dragon

/kill @e[type=ender_dragon] 

And the message appear "Killed 9 entities".