I can only imagine you are taking off in a high-interference area. Are there any radio towers/powerlines around? Where exactly are you located? I'd suggest to download WIFI ANALYZER app for android and run it on both the 2.4/5ghz frequencies to test what your smartphone can pick up. Interference should not be a problem on 5ghz at all, given the amount of channels to jump to...but it can be an issue with 2.4ghz. There's also another option to look at here:
Phantom 4 Pro - 32 Channels hack
Additionally, you can try focusing your antennas on the RC. Perhaps
buy this cheap gadget which wraps around your 2 OEM antennas and amplifies the range - NOT that you should need that for anything under 5km line of sight, but...I'm just making additional suggestions since no one has bothered to chime in and help.
Next test should be done on a calm dry day, out in a field in the middle of nowhere, with no interference to speak of. If you still have issues, consult your reseller or DJI directly for a DOA/warranty return etc. Goodluck.
RoOSTA