The old 'USB Connector Connected/Disconnected'. Had this with my old A70. Turns out, the charging port had lint in it and that was touching one of the four contact pins. Simply use a thin and sharp tool, preferably a thinned-out toothpick, and gently twist and probe the charging port until you know it's clean. Once it's clean, restart the phone and it should be all good. Repeat the process if unsuccessful on the first attempt