Why initialize_scene() doesn’t print anything the first time it’s called? Put a breakpoint in it to check if that function is indeed called the first time.
first instantiated scene is WorldMap.gd which has no such function, it is loaded fine and doesn’t need one. Although, i tried to copy this func in there, and it gives the same error.
I noticed the resource file sometimes has no data in the debugger, this way it has no game_scenes list. Seems like using load instead of preload in Constants fixed the issue, but still testing.
With respect, your instantiate code is not guaranteed to work. get_packed_scene can return null. If it does, everything after that line will fail. You could check for null and write code to handle the failure, but the approach I would take is to make sure get_packed_scene always returns a PackedScene.
As for the error you posted about, it is because constants do not have a property named game_scenes.
You did not post the code for Constants.GAME_LOCATION_LIST, so I have to assume that game_scenes is a defined list inside that constant. I have not used nested constants myself, so I can not say how or even whether that works. Regardless, if game_scenes is a constant then it should be GAME_SCENES by convention. Properties are what have all lower-case names.
If you post the actual code for your constants we can help you figure out whether the issue is in the way you defined the data or in the way you are referencing it.