How to reproduce:
1. Open the attached project "case_1285289-Project.zip"
2. In the Project Window, select the "Natori" Prefab
3. Open it in the Prefab preview mode (Double-Click on the Asset)
4. In Hierarchy, select any of the children parented under "Drawables" GameObject
5. In the Inspector, check the Mesh Renderer's Material fold out
6. In the Project Window, select all the Assets excluding the "Scenes" folder
7. Export it as a package (Right-Click->Export Package)
8. Create a separate project with the 2D template (2D is required, doesn't reproduce with 3D)
9. Import the previously exported package
10. In the new project's Project Window, Select the "Natori" Prefab
11. Inspect the previously observed Mesh Renderer materials tab

Expected result: Materials are referenced and not "None"
Actual result: Materials are not referenced

Reproducible with: 2018.4.30f1
Not reproducible with: 2019.4.16f1, 2020.1.17f1, 2020.2.0f1, 2021.1.0a10

Notes:
- Not reproducible in Windows and projects made with the 3D template