How to reproduce:
1. Download and open the project "1289310.zip" from the attached link (or alternatively use the provided TeamViewer machine)
2. Load the Scene "_primaryUI_Main"
3. Wait ~5 minutes for the initial Scene to begin
4. Click on the topmost "CAMPAIGN" button
5. In this "SELECT DIFFICULTY" menu press "Ok" (make sure "Tutorial" option is ticked off)
6. Go through the story options selecting random character traits
7. Skip the cutscene by clicking the left mouse button
8. Once in this new loading Screen put the Editor out of focus (for ex. open another application on top of the Editor)

Expected result: The new Scene loads without any issues
Actual result: The current Scene freezes and no longer loads the new Scene

Reproducible with: 2020.1.14f1, 2020.1.17f1
Could not test with: 2018.4.30f1, 2019.4.17f1, 2020.2.1f1, 2021.1.0b1 (project is complicated, takes too long to upgrade/downgrade to test)

Notes:
- Does not fail to load the other Scene when the Editor/Player is in focus (might take ~5 mins to load)