When the dragon was killed, a new portal was spawned on the base. The dragon was resting baseon the , i was in creative, i had strenght 100 thru /effect. it probably doesnt affect it, but i might aswell say it.

When I killed the dragon, like normal I expected the portal blocks to spawn in the frame under the dragon.

Instead, another portal spawned directly on top of the base structure; im guessing only because it was on top of it. I haven't tested if it spawns anywhere else, but its a bug nonetheless. I killed the dragon again, as it died the portal spot spazzed out out, spawned another portal shape out of endstone, and eventually went to as it was in the screenshot below. weird.

Steps to Reproduce:
1. get the dragon to low health and wait for it to rest on the portal
2. deliver the final blow
3. If the bug triggers, another portal should spawn on top of the base.