How to debug a UWP application on Microsoft HoloLens?

Microsoft provides a tutorial for writing your own device portal plugin. When I deploy my plugin/UWP application via the HoloLens device portal (View > Apps) to the HoloLens and try to run it I receive a message "Failed to start package !App (0x80070005)".

I've tried to debug the application as described in the tutorial (and as described in the manual). I've set a breakpoint in the "Run" method and in a callback which is triggered when a request to the device portal is received.

When I hit debug button in VS the app is deployed and the debugger seems to run (can't start another debug session or else (buttons are greyed out) but I don't see any locals, call stack, etc. When I hit the pause button I get an "Unable to break execution. No processes are currently being debugged". What am I missing?