When an ender dragon is summoned it lacks hitboxes for a single tick and as such can't be interacted with. The sub-hitboxes are located underneath the portal, at 0, 0, 0.

Steps to Reproduce

• Do /tick freeze
• Summon an ender dragon
• Step 1 tick

Observed result

• When the ender dragon is summoned it lacks hitboxes
  
• After stepping 1 tick the hitboxes appear
  

Expected result

• The hitboxes would appear immediately after a dragon spawns.