This does not happen all the time, but rarely. Looks like a race condition for me:
Message: Value does not fall within the expected range.
at System.BluetoothLe.Adapter.DeviceFoundAsync(BluetoothLEAdvertisementWatcher watcher, BluetoothLEAdvertisementReceivedEventArgs btAdv)\r\n at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_1(Object state)\r\n at System.Threading.ThreadPoolWorkQueue.Dispatch()\r\n at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()
"Message":"Schwerwiegender Fehler (0x8000FFFF (E_UNEXPECTED))"
at System.BluetoothLe.Adapter.DeviceFoundAsync(BluetoothLEAdvertisementWatcher watcher, BluetoothLEAdvertisementReceivedEventArgs btAdv)\r\n at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_1(Object state)\r\n at System.Threading.ThreadPoolWorkQueue.Dispatch()
both seem to be thrown unobserved, which makes catching them difficult.
I do not have more stacktraces atm, this mangled stuff comes from our error reporting system.