Many thanks for your reply.
Video displays then disconnects after about 4 minutes, sometimes everything disconnects but can still land the drone. I deleted/reinstalled the DJI GO 4 and got rid of the other one. I got longer video after that but it still disconnected. I'm using Apple 7 Plus for display and have the latest iOS version. I live in the inner edge of an extinct volcano, cell and wi-fi is not good. Phone is attached to the RC via the supplied cable on the side of the remote. I notice there is a USB port in the middle of the remote, can I use that instead of the other one?? I don't know what height or distance I was flying. Hope this is sufficient.