Brought a P4 the other day and went through the connection nightmares (17hrs straight) I have read others experinceing and tried all usual fixes with no sucess other than a connection once and then not again yet was working fine on my mrs old galaxy S4.

FIX:Ensure drone is on latest firmware by pc update over micro usb
1. Enable usb debugging
2. Remove Dji Go 3.0
3. Download Dji Go 2.8.2 APK (from a clean source) and install
4. Connect phone to a working pc and check you can swap form camera to mtp (or other options your model may have like mass storage or software)
5. Switch on RC then Drone and connect a borrowed working phone that connects and remain on the screen that says aircraft connected/camera
6. Open Dji Go 2.8.2 on your device and while the other phone is connected remove the micro usb and place into your device as fast as you can without causing damage, this should now trigger the option to always launch Dji Go each time the RC is connected (select yes in the tick box)

Your device should now connect to the RC and P4 (possibly other models too) you may need to switch between camera and mtp now and again with Dji app closed but connected to RC then restart connection process and no longer need the 2nd working device to swap out...

I tested connecting several times after this process using only my device with about a 75-90% hit rate on first boot from phone, drone and RC powered off.



Note I used a S4 but other models may work and not sure about cross platform to IOS but maybe others can try and post results, hope this helps some birds to stretch their wings.

Someone mentioned 2.8.2 had issues with pixels going funny and 2.8.3 may be the better option, I know some mentioned 2.9.0 but I had no luck with that update