Forerunner 945 looses connection and do not reconnect to Garmin app in iPhone.

Forerunner 945 looses connection and do not reconnect to Garmin app in iPhone. It might be related to loosing connection due to distance, but it doesn't reconnect. Only way to reconnect is to forget Forerunner in Bluetooth connections, start pairing in the Forerunner and start Garmin app in the iPhone. After pairing connection works and data synchronize, but it lasts only few time and then the process need to be repeated to reconnect.

Is there a trick to ensure continuous connection and reconnection to get data synched automatically?