How to reproduce it:
1. Open the user's attached project "Upgrade.zip"
2. In the menu bar click "shoutr lab" > "Export for Android"
3. Observe the Console window

Expected result: Project is successfully exported
Actual result: Exception "InvalidOperationException: The build cannot be appended." appears

Reproduces on: 2019.4.30f1, 2020.3.19f1, 2021.1.22f1, 2021.2.0b12, 2022.1.0a6

Notes:
- Not reproducible when Exporting project via Build Settings
- Exception appears in line BuildPipeline.BuildPlayer(scenes, pathBuild, BuildTarget.Android, BuildOptions.AcceptExternalModificationsToPlayer);