Okay try this:
Upgrade to 1.8.x, downgrade to 1.6.x how you did it. Then downgrade the drone WITHOUT the controller on to 1.5.x. Try flying again. Dont forget the calibrations.
Downgrade went successfully, AC is now version 1.5.70+. I didnt connect the RC after downgrading from 1.6 to 1.5 so the remote should stay 1.6. App version 3.1.11, im gonna test the distance tomorrow. Im flying the P3S too btw with the antenna mod.