Check the attachments to learn more about this.

Steps to Reproduce:
1. Enter the end, and kill the first dragon.
2. Type /tick freeze and place down the necessary end crystals to revive the dragon.
3. You'll see once you finish Step 2, the dragon respawn process starts, which isn't frozen by /tick freeze

Expected Results:
The dragon respawn process should get frozen by /tick freeze.

Notes:
This bug exists in carpet mod, too.