Sorry to hear this. Do you have the most recent version of the app installed? Is anything else running in the background while you’re flying the missions (I find this happens if I have 20 or so other apps still open on my phone)?
I have the most recent versions of the DD app, DJI Go App and the iOS for the phone. Drone Deploy was running on the foreground and DJI Go was on the background. Other than these no other applications were running.
EDIT: seems that DJI Go is the culprit since it uses the phone GPS all the time, even on the background. Will do a flight later today - if weather allows me to since it’s raining cats and dogs in here - and report back on that.