Do you fly in airplane mode but wifi on or off? I ask as I recall using an iPhone 7 with wifi off (memory not failing me), which I traded up to an iPhone Xs. The Xs does not connect with wifi off. However, with the wifi off you have the danger of the iPhone attempting to connect to the strongest signal (which it does by default), which means trouble with the done's connection.
Of course, to fly with wifi off means the app can access the wifi directly.
Of course, to fly with wifi off means the app can access the wifi directly.