Hello there!
I tryed to downloaded this file, but that's an project file from C2, and I'm not using C2 anymore, and C3 apparently don't open project files like that one for some unknow reason.
Anyway, you could upload the single file from your project, that'shoudld be more easy to do.
Just reading what you said there, I can make a simple question.
Do you used the Solid behavior in the walls? Otherwise, the platformer behavior will have no reason to collide with this sprite.