I had the same issue today, with a phantom 4 pro v2. Ran the survey (a small test) once with a single battery, then ran it again to see how a battery change would work. drone returned home when it got to 30%, landed, I swapped the battery, selected “continue” the survey, went through the checklist fine, then when I selected “fly”, nothing happened. Drone just sat there, no prop movement, nothing.
The screen indicated nothing wrong, but the drone status in the upper left said “Drone connected, GPS mode”, but the “start flight” button lower left was greyed out and not active.
I tried rebooting drone deploy and the drone, attempting to “continue” the mission, but nothing happened (repeatedly). The only thing left in this test was to fly the perimeter (3D enhanced) but nothing happened.
As far as I can tell from this and other threads, this is a common issue and there have been no solid solutions. thoughts anyone?