I am unable to deploy my Windows Phone 8.1 app (XAML, appx) to Nokia Lumia 920 running Windows 10 Mobile v10512. The deployment just fails with:
Error : DEP0001 : Unexpected Error: Element not found. (Exception from HRESULT: 0x80070490)
Deploying WP8.1 app to WP8.1 devices work. Deploying Windows 10 UWP apps on that Windows 10 Mobile device work as well. Even deploying that WP8.1 app on Windows 10 Mobile Emulator works.
I got machine running Windows 10 x64, Visual Studio 2015 with Windows 10 SDK v10240, all RTM.