I have a P4P using iPhone 6 plus with iOs 11.02 installed.  Not sure if the App is to blame for this but here is what I have noticed.
Turn on the RC
Turn on the AC
Phone was already on and App Running before I turned on RC/AC

App shows disconnected in bottom left corner.  When you enter into the app no Camera View, No Data to view or change, nothing. But you can start the motors with the RC.

Turned off RC and AC and recycle them.  Still no joy.

Finally turn off everything including the iPhone.  Restart iPhone, RC then AC.  It now is working.

I think it was the iPhone App.  The reason I say is because I tried several times to recycle the power on the RC/AC and nothing.  Only after I restarted the
iPhone did the Camera View and Data come back.

Anyone else noticed this.

Yes I posted a reply to a similar previous thread two days ago. Rebooting the OS device often helps to sort out problems. It seems to be the new OS 11 is creating some problems, my updates work fine, ipad, iphone and Litchi.

I made the mistake of upgrading to iOS 11 when it first came out... nothing but issues with DJI GO. I downgraded iOS to 10.3.3 and the issues vanished. So, if you want problem free then revert back to iOS 10.3.3 and hold off on upgrading to the latest as soon as it is released... if you want to be a beta tester with your expensive equipment then update to the latest versions and risk a crash at your expense. It is that simple.

iOS DJI Motto: "If it ain't broke then don't break it with an update."

Bob Brown Posted at 2017-10-7 04:51
I made the mistake of upgrading to iOS 11 when it first came out... nothing but issues with DJI GO. I downgraded iOS to 10.3.3 and the issues vanished. So, if you want problem free then revert back to iOS 10.3.3 and hold off on upgrading to the latest as soon as it is released... if you want to be a beta tester with your expensive equipment then update to the latest versions and risk a crash at your expense. It is that simple.

iOS DJI Motto: "If it ain't broke then don't break it with an update."

I tried using the IPSW File at this site, but I get an error message in iTunes and it won't let me revert back to 10.3.3  You suppose Apple is preventing this on my iPhone 6s Plus?

http://osxdaily.com/2017/07/19/ios-10-3-3-download-update-ipsw/

This is the message.  I think Apple is preventing this.

And this information

Just to verify, what's the current version of your DJI GO 4? Have you tried to re-install the APP?

DJI Susan Posted at 2017-10-7 22:53
Just to verify, what's the current version of your DJI GO 4? Have you tried to re-install the APP?

Version 4.1.12

BlueBirdTN Posted at 2017-10-7 05:24
I tried using the IPSW File at this site, but I get an error message in iTunes and it won't let me revert back to 10.3.3  You suppose Apple is preventing this on my iPhone 6s Plus?

http://osxdaily.com/2017/07/19/ios-10-3-3-download-update-ipsw/

Appears 11.0 and 10.3.3 are no longer being signed by Apple.
Glad I downgraded when I did!

same case with me..i use ipad mini 4 ios version 11.02 & dji go 4 version 4.1.12..
dji go 4 app disconnect with aircraft..rc & aircraft link..

BlueBirdTN Posted at 2017-10-8 04:04
Version 4.1.12

You might try changing the cable between the RC unit and phone, sometimes the cable is to blame for lack of connection issues.

Try turning on the RC and the AC first, with the phone disconnected from the RC. Once you get the green light on the RC, plug your phone in and launch the dji go app.

DJI Susan Posted at 2017-10-7 22:53
Just to verify, what's the current version of your DJI GO 4? Have you tried to re-install the APP?

SUsan, I don't know if this is related, but I have read that iOS 11.3 is optimized for 64-bit Apps, and 32-bit Apps will not work with it anymore. My question now is:  Is DJI GO 4 a 64- or a 32- bit App?

DJI GO is a multi-target App, means it can running both on arm64 and armv7. The connection problem seems a known issue in iOS 11.0, 11.0.1 & 11.0.2, now we are talking with apple about this issue and hope it can be fixed on iOS 11.1

Antonio76 Posted at 2017-10-14 05:01
SUsan, I don't know if this is related, but I have read that iOS 11.3 is optimized for 64-bit Apps, and 32-bit Apps will not work with it anymore. My question now is:  Is DJI GO 4 a 64- or a 32- bit App?

Antonio, 14# is the reply from our engineers, please take it for reference.

DJI Susan Posted at 2017-10-17 02:30
Antonio, 14# is the reply from our engineers, please take it for reference.

Thanks Susan

I've got a P3P and am having same issue.  Works OK with iPhone 7plus running the IOS 11.0.3 but won't work with the latest iPad 2017 version running the same IOS.  Not happy but seems we have to wait.

I can confirm this was resolved with iOS 11.1.  Did not have to do anything special after upgrading iOS.  The connection between the app and the RC just works as expected now.

DJI Susan Posted at 2017-10-7 22:53
Just to verify, what's the current version of your DJI GO 4? Have you tried to re-install the APP?

I am having this issue with my P4PRO what do you suggest ?? thanks in advance im at a loss

FLYWAY2HI Posted at 1-18 17:38
I am having this issue with my P4PRO what do you suggest ?? thanks in advance im at a loss

currently 4.0 dji go app

FLYWAY2HI Posted at 1-18 17:38
I am having this issue with my P4PRO what do you suggest ?? thanks in advance im at a loss

and have re-installed a million times