I see the very same issues. Also tried digikam, but same issues arise - connection fails, the camera discards the connection, and you have to start all over again. The message there is “Failed to connect to the camera. Please make sure it is connected properly and turned on.”. Which it is 
Gphoto is gphoto-2.5.28p0, Camera firmware is 2.50, digicam is 8.1.0.