After successfully packaging the project using your posted settings, I asked a teammate to review the issue in case I’ve missed something:
He noted that where you applied the “rename” solution:
I did the trick where you rename the folder, run project, rename it back and run the project (the official proposed solution)…
-You are not suppose to rename it back. Instead you should use a different name altogether like, “GunBunny2.”
This should resolve the “Externally Referenced Warning” and may result in fixing the map load error.
Please try this and let me know your results.