@Roddyb The app doesn't control/affect the devices connecting to wifi once they're setup.  On all 6 of the HS100s the wifi connection LEDs were flashing amber?  If so, you must have changed something in your network, the app can't break them.

Perhaps they were wifi connected but they couldn't be found by the app?  Often they get connected but the app can't find them because the phone rejoins the wrong part of your network.  Restart your router, then shut down your 5GHz SSID and any APs.  If the HS100 LEDs are flashing setup one at a time - leave the others powered off.  If not flashing, join your phone to your 2.4GHz SSID and try searching for them with the app.