Reproduction steps:
1. Open "Bouncy Ball I.zip" project
2. Open any script (AreaAxisComposite.cs)
3. Enter Play mode
4. Write a trivial code line ("public Transform test;")
5. Focus Unity
6. Notice spam of "NullReferenceException" errors
7. Exit Play mode
8. Editor Crashes

Expected Result: Editor doesn't crash/spam errors
Actual Result: Editor crashes/spams errors

Note:
Sometimes the Editor doesn't crash, only spams errors
Sometimes there's no spam of errors, only two, but the editor crashes

Two errors:
"System.InvalidOperationException: Burst compilation can't be switched on while in PlayMode
Loading GameObjectEntity in Playmode but there is no active World"

Reproduced with: 2020.1.0a13, 2019.3.0b11, 2019.2.13f1
Did not reproduce on (Needed Packages are not present): 2018.4.13f1, 2017.4.35f1