I'm using a Samsung Galaxy Tab A7 and I see this happen quite often. I usually cycle the power to the ADSB receiver rather than the A7 so I don't lose the current 'Flight Trail' data and that will usually restore the ADSB data but so will cycling the iFly app. While the ADSB data isn't showing, the other data from the receiver is present, like AHRS and pressure altitude, so communications with the receiver is occurring.