I got the phantom 4 pro 2 days ago and I haven't been able to fly. I open it, did all the firmware updates on the DJI assistant 2, updated the aircraft first then the remote controller. and after doing an IMU calibration as I always do with my other birds the remote lost connection and I haven't been able to relink them after the imu calibration. I have spent hours doing all kinds of fixes but nothing seem to work, rc bottom conbinations, aircraft linking bottom, android and ipad, different cables, downgrading firmware, reinstalling DJI 4.0 app etc.... and nothing works. It so frustrating, specially after having DJI products for the past 2 years, inspire 1 raw, phantoms and never having issues. At this point I am just going to return the bird to amazon and get a new one.

Both RC and AC were upgraded successfully, right? Have you tried to refresh the firmware or reset it to factory default then upgrade to latest again?
You can calibrate IMU successfully, but cannot link them after the calibration, right?
The LED on remote keep solid red?

Yes, I reset to factory settings and nothing, rc has red light and aircraft orange light.

same problem of you man and we are not alone !! i read 4 posts with same problem !!!!

Fixed mine.

Not sure if this will help, but I toggled frequencies 5.8 to 2.4, rebooted the RC, and my RC linked to the drone. I hope this helps.