Flew with the mini 4 last night. No crashes, clear and flawless video streaming.
I flew up to ~3,000 ft horizontal at 150 feet and never lost video.
Note: i also had a MAXXUAV un-boosted antenna on the controller. For $130, it is a great solution.
Are you on 4.1.0 DJI go and iOS 10.3.2?