So according to you there are two things inside the shell? A proton and, what? The thing which you steadfastly, ignorantly and rather stupidly refuse to acknowledge is that the proton experiences a net zero force from the shell regardless of its location within the shell, as a consequence of the shell theorem, and therefore the arrangement is unstable. Simples!
There doesn't have to be two things inside the shell. The single proton will do. And yes, it is as you say, the proton will experience a net zero force from the shell. The kicker is this: any point on the shell will now experience an inward force from the central proton. Similarly, if there happened to be another particle inside the shell, it too would experience a non uniform field emanating from the proton.