The [LINKLOSS] warning message appears on the watch display when the Bluetooth connection between the watch and phone is about to be lost due to any one of the following reasons: the watch and phone are too far from each other, the phone is turned off, radio interference, etc. A loss of connection will cause the watch to return to the Timekeeping Mode.
To re-connect, move the watch and phone so they are near each other and then hold down the watch’s (B) button for about 0.5 seconds.

• If “Tone” is selected for the GBA-400+ “Link loss alert” setting, the watch will beep when link loss occurs.
  Configuring Watch Settings