Happened to me for the first time yesterday. Just after flying out nearly 3mi, I was just flying close by on the 3rd battery. Up about 40ft over water and about 2500ft away...Complete signal loss. I thought I heard a splash and thought the worst. Hit RTH after closing DJI Go and restarting the app on my iPad
Air 2 didn't resolve. Like a miracle, after a few mins I heard the sweet buzzing sound of the drone approaching. Needless to say, I'm a little hesitant to push this thing now.
EDIT: Forgot to add that mysteriously, my flight log data ends right at the point of the signal loss. So the track of the RTH is not displayed in the DJI Go App. I will have to analyze the log files later to see what's going on here.