You pFactory reference is null. But you do initialize it, so why is it null? Because your code is broken, it does this:

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    ... some code
    case WM_SIZE:
        {
           ... some code
        }
        
    // there is no break here!
    // first call to WM_SIZE falls down to WM_DESTROY which destroys your pFactory...
    
    case WM_DESTROY:
        DiscardGraphicsResources();
        SafeRelease(&pFactory);
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;

Just add a break before WM_DESTROY.