How to reproduce:
1. Create a new project
2. Create Canvas make it World Space
3. Add Button to it (Make sure it is seen in Game view)
4. Select Maximize on play in Game view
5. Save the scene and play it
6. Stop the scene, Unity will freeze

OR
- Open the project
- Open "CombatScene"
- Click Play
- After the project is running, click Play a second time to take it out of Play mode
- Result: Unity freezes 100% of the time