I was taking some video of construction and cranes yesterday and was out of sight of the drone. Where I had to park prevented me from seeing the drone due to another building being built in front of me. I was circling the cranes at about 400' high when the video feed locked up. All other items in the DJI GO app were working. Distance, height, speed etc.. I figured I could not do return to home because I didn't know if there were other buildings that were that high or not. I could not see the drone to bring it back so was afraid I would run into something. I finally had to walk around until I could see it. So my question here is how safe would it have been to close the DJI GO app and reopen it while in flight like that? I think others have said they did it but honestly when I'm 1000' away and 400' up it's a bit unnerving to kill the app and restart it.