How to reproduce:
1. Open the attached “1388175.zip” project
2. In the Project window select “AddressableAssetSettings.asset”
3. In the Inspector add an “Asset Group Template” by pressing “+” under the “Asset Group Templates”

Expected result: Asset Group Template is added
Actual result: 2 warnings appear in the Console and the Asset Group Template is not added

Reproducible with: 1.19.9 (2019.4.34f1, 2020.3.25f1), 1.19.15 (2019.4.34f1, 2020.3.25f1, 2021.2.7f1, 2022.1.0b2)
Not reproducible with: 1.19.6 (2019.4.34f1, 2020.3.25f1)

Errors:
Invalid AssetDatabase path: /Assets/AddressableAssetsData/AssetGroupTemplates/test.asset. Use path relative to the project folder.

Failed to load Asset at /Users/mantas.kandrotas/Downloads/Adresssibles/Assets/AddressableAssetsData/AssetGroupTemplates/test.asset.