ok, I boiled down the project as much as possible and uploaded it (25MB):
When loading it in the editor, it will ask you to rebuild missing dlls. Just rebuild, it should work.
When the editor opens,it will complain about missing content in the StarterContent. Just ignore the warning, the projectile will not be instantiated.
To test:
1.) start simulation. A box should fall down near your character.
2.) hover the mouse over it. Mouse cursor should change. Click on it. Box should disappear.
3.) Stop Simulation.
4.) open Blueprint: /Game/FirstPerson/Blueprints/FirstPersonCharacter’
5.) At the end of the execution queue of Event Begin Play SetVisibility to Visible
6.) Compile and restart simulation.
7.) The box does not react to the mouse now as it should be. This is the bug.
The menu that is created at 5.) is just a UserWidget that contains a canvas. It is probably swallowing all mouse events to the world.