Devices list may be outdated if scanning is stopped
Devices that aren't visible for bluetooth adapter anymore can still be shown in the UI, if they got lost after scanning was stopped. Trying to connect to them would cause an error.
I think the best way to fix it is to remove start/stop scanning button, and just toggle it whenever the devices view is opened/closed. The button is deceiving anyway, since it doesn't actually switch the scanning mode on the bluetooth adapter, but just starts/stops listening to the adapter events in the app.