How to reproduce:
1. Open user's attached project "L10nBug.zip"
2. Open the "Medieval Environment" Scene
3. In the Hierarchy window select "Shield Right" > "TextMeshPro Text"
4. In the Inspector window locate the "Localize String Event" Component and its Local Variables field
5. Select the List item and remove it
6. Create a new Object Reference Local Variable and in its Object Reference field select the "ControllerButtonLocalizedString" script
7. Save the project and reopen the Scene
8. Repeat steps 3 and 4

Expected result: Local Variable item contains the same parameters
Actual result: The Local Variables item's Object Reference is replaced with "Empty"

Reproducible with: 1.0.0, 1.0.5 (2019.4.21f1, 2019.4.27f1)
Not reproducible with: 1.0.0, 1.0.5 (2019.4.28f1, 2019.4.34f1, 2020.3.24f1, 2021.2.7f1, 2022.1.0b2)

Notes:
- Similar to case https://issuetracker.unity3d.com/product/unity/issues/guid/1387617
- When downgrading from not reproducible version, the issue no longer reproduces but errors in Console still occur