New out of the box, first flight, DJI Go 4 app gives me a warning that the vision system needed to be calibrated. I did a quick cal with the app, then when I got home calibrated with the DJI Assistant 2 app.
Being on Windows 10, I had to disable driver signature enforcement and reinstall the DJI Assistant 2 app to get the right drivers needed for calibration to install. I didn't think I would need to since upgrading my firmware worked just fine, but apparently the vision calibration requires a different driver.
Anyway, once calibrated, the warning went away and my subsequent flights were just fine. Oh and by the way, I was also prompted to calibrate my compass.