To reproduce:

1. Download attached "case_1202254-SerializationBug 2.zip" project in Unity
2. Check Console window

Expected results: No Errors or Warning are thrown
Actual results: 4 Errors are thrown:

"Unsupported texture format - Texture2D::EncodeTo functions do not support compressed texture formats."

Notes:
- If you start reproducing these Errors, you will reproduce it almost everywhere - to stop it from reproducing open it first on 2019.3.0f3 and then on 2019.3.0f2 (I don't know why but then it fixes itself) or just extract it again
- This issue was found by testing this https://fogbugz.unity3d.com/f/cases/1202254 case

Reproduced on Unity 2019.3.0f5, 2019.3.15f1, 2020.1.0b10, and 2020.2.0a12
Not reproduced on Unity 2019.3.0f4
Regression on Unity 2019.3.0f5