It happened to me every time I flew my P4 with my iPad Air (the last iOS 11 version). Then, I switched to my Nexus 5 (Android 6, an old, but a very reliable phone) and the image is just perfect with DJI GO 4. No glitches, no app crashes, everything so much better than with the iPad. In the future, I’m going to test an older iPad 4 with iOS 10, in order to see if this is the cause of the problem or not, but if I want a comfortable fly, I’m sure I will use the Nexus phone.
I think iOS 11 is unusable in slightly old devices.