I'll jump in as I have a love/hate relationship with the app. The grill works just fine without using the app, but as was said "I paid for it." There is some hidden connections at work. First the grill only connects directly to the phone/tablet through bluetooth to set up wifi. When connected to wifi, even without app open, the grill is connected to an IoT Server (cloud). So there is an added level of connection that can go wrong.
As for updating the grill, the best luck I had was to plug in grill BUT do not press the power button. The grill controller is powered up. That is the "state" that I have the best luck at updating the grill.