First off, make sure all other apps are close. The DJI Go app and all other apps that connect to the aircraft should be closed so that Map Pilot is the only app trying to use the connection to the device.
As the error message says, this error is not documented by DJI so we have been unable to figure out how to stop it from occurring. The only way we have found to get it to clear is just to try to reload the mission again a few times. It usually works.
Hopefully this error will not be present in the next version. We haven't seen it yet in our testing.