Reproduction steps:
1. Open the attached project "1376153_case.zip"
2. Go to Project Settings > Editor.
3. Navigate to the "ETC Texture Compressor" settings and in the "Behaviour" section select Custom
4. In the "Best" section select "ETCPACK Best" and save the project
5. Navigate to the project folder and go to the Project Settings Folder and open EditorSettings.asset with a text editor
6. Observe the m_EtcTextureBestCompressor value (it will be either 2 or 5).
7. Go back to Project Settings > Editor and click the "Best" compressor setting and select the setting which it already has ("ETCPACK Best")
8. Save the project again and look at the EditorSettings.asset again

Expected result: The value of m_EtcTextureBestCompressor stays the same
Actual result: The value of m_EtcTextureBestCompressor will have changed from 2 to 5 or from 5 to 2

Reproducible with: 2020.2.0a8, 2020.3.23f1
Not reproducible with: 2019.4.32f1, 2020.2.0a7, 2021.1.0a1, 2021.1.28f1, 2021.2.3f1, 2022.1.0a15

Notes:
- Selecting "ETCPACK Best" as the best compressor, then saving the project, then looking at the EditorSettings.asset again, the value will keep changing back and forth between 2 and 5, even though the same option is selected
-The issue reproduces on Standalone and Android platforms