UE4 Action RPG Template Asset Manager Error

First of all, I am Korean, so please understand that my English is not that good.

I am making my own game based on ‘Action RPG template’ provided by UE4.
Almost finished making the game, but the problem was the creation of the weapons equipment system, the “Inventory” system.

I didn’t make any modifications to the basic function of the template (although I added some C++ functions, there are no modifications to the basic C++ code).

As you can see in the picture above, despite the presence of “WEAPON DATA ASSET,” “DATA ASSET” is not reading,
and “ITEM CAST” only produces NONE’s value from the code of the main character of my game.

Can anyone guess what the problem is?

I tried to fix the problem for a week, but it couldn’t be solved, so I’m uploading it.

Thank you very much if there is anyone who can tell me.
I need your kind help.