I can tell you that the issue is not specific to DD. I fly three of the Mavic Pro's using iPhone 7Plus and also using the iPad Pro. I can tell you that there were some issues in the past but this was related more to the update in firmware from DJI. Even Litchi published a month ago that their software was having issues with the DJI firmware update but has since released a comment stating that the new update from DJI fixed it (or something like that).
Mavic Pro is a bit tough at times but this is mainly due to the fact that it likes to control ever aspect of the drone. Meaning, have your tried to fly DD without accessing the Mavic APP? This is how I do it and I see no problems. However, when I have the the Mavic App (DJI4) running in the back, I do notice a few times where I do not necessarily have control with DD.
Try connecting to the system without opening the DJI4 APP and then see if that helps. If not, turn off the automatic settings on the DJI camera settings and then run the DD software. If that does help, let me know and we can do a live video so set yours up the same way I have mine and we can see if it works then.