How to reproduce:
1. Open the attached project 'Editor_UI_Test'
2. Open the project's directory in File Explorer
3. Delete the Library (skip files when it asks you to)
4. Return to the Editor

Expected result: Library rebuilds and nothing happens to the Editor
Actual result: Upon returning to the Editor, Editor UI has missing borders for windows and a lot of other elements are missing

Reproducible with: 2019.3.0a9
Not reproducible with: 2017.4.30f1, 2018.4.3f1, 2019.1.9f1, 2019.2.0b9, 2019.3.0a7

Note: Mentioned 'other' elements include images for types of messages in the console, sliders, dropdowns, overlapping error text and more.
Note 2: After the issue the project may not open again, so if the attached project does not open, create a new default one, this happens regardless of the project.