What I expected to happen was that when quitting the game during the ender dragon summoning sequence, the process should continue after logging back on.
What actually happened was that when quitting the game during the summoning sequence and then going back on, it stops altogether while the portal is still broken.
Steps to Reproduce:
1. Have the ender dragon already killed
2. Do the process to summon the end dragon again
3. During the process of re-summoning the end crystals, quit the world
4. Go back on to that world
Duplicate of MC-91636.