I was flying my Phantom 4 Pro this past Saturday and i reached 150ft in altitude.  The remote kept on beeping as if it was sensing something, and I could not control the drone.  I tried to fly forward, backwards and it would suddenly stop as if there was some obstacle.  Remember i'm at 150ft up in the sky and there is NOTHING around, no trees, no walls, no wires, no towers.  I had to "disable" the obstacle avoidance to return it home, and I landed. I tried again withe the obstacle avoidance enabled, but the remote kept on beeping and the drone didn't fly in any direction.  What's going on?  Should I take it for check? repair?  This drone was given to me as a replacement of a CRASHED drone that fell off the sky for no reason!!!
Did I get damaged goods?  

Possibly the sun has disturbed the sensors, have seen this myself and a lot of similar reports.

Solution is as you did to disable OA system.

I would suggest try calibrating the RC first, then perhaps VPS using DJI Assistant 2, make sure the sensors are clean first.