If your render distance is below 10, upon entering The End the ender dragon won't spawn.
This could affect people with low end computers/laptops.
Steps to reproduce:
1. Create a new world
2. Set your render distance to 9 or below
3. Go to The End (setblock ~ ~ ~ end_portal)
4. Notice the lack of a dragon
5. Start increasing the render distance (10 or higher) until the dragon spawns
Sorry if this has been reported before, I couldn't find it when I searched around.