I’m not convinced there is a bug here. Launch does a cooked build. Play does uncooked. If you are referencing your other levels by string, it won’t cook them because the cooker doesn’t know (unless you tell it with some settings that I believe are not exposed in 4.7 yet).
When you say Standalone, do you mean the Standalone mode under Play? That isn’t cooking the data, so all the maps should be there. I want to verify explicitly what modes/buttons you are using for when it breaks vs works.
Josh