How to reproduce:
1. Unzip the attached user's project ("wiros-2d.zip")
2. Delete Packages/2D Entities folder because it contains the potential fix already
3. Delete the Library folder
4. Open the project
5. Load "SampleScene"
6. Select "WorldTest" subscene
7. Notice the error in the inspector

Expected results: When an Asset is in a Package, the CommonAuthoringUtils.GetFullAssetPath method deals with assets outside the Asset folder
Actual results: When an Asset is in a Package, the CommonAuthoringUtils.GetFullAssetPath method will return the wrong path as it assumes it is in the Assets folder.

Reproducible with: 2D Entities 0.29.0-preview.3 - 0.31.0-preview.3 ( 2020.2.3f1, 2021.1.0b3, 2021.2.0a3)
Could not test with: 2018.4.31f1, 2019.4.18f1 (Errors downgrading)