Then you should use the Qt resource system to embed the shader in your application. You current shader files are accessible on your host. When you start your application on your device, they won't be there.
Another interesting development: I tried running on another machine with the Qt toolchain installed, and the program worked. So it appears it is still reading something from the filesystem that is not on a regular Windows machine, but I don't know what that might be. I did package all the qmldir files needed for Qt Quick to work.