Editor freezes on recompilation when Custom window that references a VisualElement is open

How to reproduce:
1. Open the "case_1355141" project
2. Open the "Window > Asset Hive" custom EditorWindow
3. Write a comment anywhere in any custom script file in the project
4. Observe the Editor behaviour
5. Observe the Console Window output

Expected result: the Editor doesn't freeze
Actual result: the Editor freezes, and after a minute of freeze, error messages appear in the Console window

Reproducible with: 2019.4.29f1, 2020.3.16f1, 2021.1.17f1, 2021.2.0b7, 2022.1.0a5

Note: the custom window includes a property that derives from VisualElement. During assembly reload that property is serialized, even though it is private. This puts the window into a bad state freezing the editor. Putting the [System.NonSerialized] attribute on the property avoids the freeze by making sure it is never serialized during assembly reload.