My app's still running fine too. It could be a network issue. Try this;
Switch off your AV receiver (at the plug too, not just standby)
Reset your router. Most routers have a very small hole marked 'Reset' which you need to press with the end of a paperclip or something equally small. Keep it pressed in for about 20 seconds.
Leave your router to re-boot for a few minutes.
Then switch your Pioneer AVR back on. Then re-open the app and see if it connects. All the above has done is prompt your router to re-introduce itself to any devices showing on your network. It's worth a try. Beyond that, I'd double-check the connections of your ethernet cable to the router.