Three days on this, and I believe there's a race condition between adb and the emulator. On a request to run an app, with no emulator already running, you see the "Initializing ADB", then the emulator choice, it starts and you get "Waiting for target to come online". An adb kill-server, or a kill -9, or an "End Process" of adb with the task manager will cause adb to die, restart, your APK installs and you're good to go. It does seem funky to me that an "adb kill-server" causes adb to die and then restart here, but that's another mystery, maybe.