How to reproduce:
1. Open the attached project
2. Open 'TestStruct.cs' script from the Project window
3. Make some insignificant changes to the script
4. Return to the Editor

Expected result: After recompile, there are no Console errors caused and Editor GUI does not break.
Actual result: After recompile, there are ReflectionTypeLoadException and ArgumentException errors in the Console and Editor GUI starts to break after some time (or after forcing the script to recompile again).

Reproducible with - 2018.1.0a4, 2018.1.7f1, 2018.2.0b11, 2018.3.0a4
Not reproducible with - 2017.1.4p2, 2017.2.3p1, 2017.4.6f1, 2018.1.0a3

Notes:
- The reproduction steps that break Editor GUI are not consistent, it usually involves moving around GUI elements in the Editor window. However, ReflectionTypeLoadException errors are always reproducible.
- The Console errors are also reproducible when building the project and running the build.

Fixed in 2018.3.0a8