Reproduction steps:
1. Open the attached project "SerializeReference" and scene "MaterialList"
2. In the Hierarchy, select "MaterialList" and make sure "Test1", "Test2" materials are attached to the "Materialcells" list
3. Enter Play Mode and see both Materials being logged in the Console
4. Build and Run the project.
5. Open Player Log by clicking the three dots in the right corner of the Console window and selecting "Open Player Log"

Expected result: Both Materials are being logged in the Player Log
Actual result: Materials are null

Reproducible with: 2019.3.0a2, 2019.3.0b6, 2020.1.0a8
Could not test with: 2017.4.33f1, 2018.4.11f1, 2019.2.8f1, 2019.3.0a1 (SerializeReference inaccessible due to its protection level)