Just upgraded, went for a flight with the iPad mini 4, image from the drone looked like someone smeared something on the lens, no more crisp image. Downgrading now hope nice crisp image returns to iPad.
Try unplugging otg cable from rc, then turn on rc and then spark, wait for the red light on the rc to turn green, then plug otg cable back into rc. Device you are using should now be able to use dji go 4 app.