The ender dragon's sub-hitboxes (the green ones) are positioned at 0, 0, 0 in any dimension until the dragon starts its first AI tick. For dragons with NoAI NBT set, the dragon will never have a hitbox. For naturally occurring dragons, this will result in the dragon lacking any sub-hitboxes for 1 tick.

Steps to Reproduce:

Method 1:

• Tick freeze the game:

  /tick freeze
  

• Summon or spawn an ender dragon
• Step 1 tick

Method 2:

Run the command:

/summon ender_dragon ~ ~ ~ \{NoAI:1b}

Expected Behavior:

The dragon would have all necessary hitboxes and sub-hitboxes when spawned.

Observed Behaviour:

The dragon has only has it's outer (white) hitbox, but that hitbox cannot be interacted with or attacked.