Fatal Error Cooking (0]LogWindows:Error: begin: stack for UAT)

Hey ,
thanks for your continuos support! We have managed to package the game, after removing a Blueprint from the Level and spawning it on begin play. The game didn’t cook with this asset inside of the level. We don’t know why. We did find this work around, but it would be nice to know why this happened in the first place. Here is our project: Download
The asset in question is called “MediaPlayerBlueprint”