Repro steps:
1. Open the attached project in 2019.3.0a8 or an older version
2. Close the project and open it in 2019.0a9 or a newer version
3. In the "SampleScene" click on the "CustomCube" object
4. In the Inspector window, click on the Cooking Options in the Mesh Collider component

Expected result: All default options are checked and no error is thrown
Actual result: The "Use Fast Midphase" is unchecked and an error is thrown: "This MeshCollider (GameObject: 'Cube2017.4' Mesh: 'Cube') requires the mesh to be marked as readable in order to be usable with the given transform."

Reproducible with: 2019.3.0a9, 2019.3.0b1, 2020.1.0a2
Not reproducible with: 2017.4.32f1, 2018.4.8f1, 2019.2.4f1, 2019.3.0a8

Notes:
1. Read/Write Enabled option in the Import Settings for the used mesh needs to be unchecked
2: Resetting the component or checking the Read/Write Enabled option fixes the error