How to reproduce:
1. Create a new project or open an existing one
2. Create any UI GameObject
3. Save the automatically created EventSystem GameObject as a Prefab
4. Delete the Canvas GameObject and the EventSystem GameObject
5. Create a new UI GameObject

Expected result: EventSystem GameObject is automatically created
Actual result: EventSystem GameObject is not created

Reproducible with: 2018.3.0a6, 2018.4.13f1, 2019.2.14f1, 2019.3.0f1, 2020.1.0a15

Not reproducible with: 2017.4.35f1, 2018.3.0a5

Notes:
Reopening the project and creating a new UI GameObject will work as expected.