Welcome to our OGS family!
I found your EGS.vtu has 4 kinds of material, but in your EGS.prj you only give medium id="0" and medium id="1"(only 2 kinds of material’s property). That is the problem, I think.
You must give each material corresponding material’s property in your prj.
For more information you can find here, A small question about the '.prj' file.
Hope it can help you
Rui