DIAGNOSIS The connection between the app and the ice maker is notoriously glitchy. It often loses the pairing after an app update or a router change.
FIX You need to delete the device from the SmartHQ app and re-pair it from scratch. In the app, go to your device list, find the Opal, and remove it. Then, on the ice maker itself, press and hold the "Light" button for 10 seconds until the front lights flash—this puts it into Bluetooth discovery mode. Now go through the "Add a Device" process in the app again.
IF THAT DIDN'T WORK Make sure your phone's Bluetooth is on and you're within 10 feet of the machine. Also, some users have had success by turning off their phone's WiFi temporarily during the pairing process, as the 2.4GHz signals can sometimes interfere.
HEADS UP The app connectivity is mostly for remote start/stop and clean reminders. It doesn't control any critical functions. If you can't get it to reconnect, you're not missing much—you can do everything manually on the machine itself.