Can airflow reverse over the flight surfaces of a uav in high wind conditions
It is possible, but only if there were a very sudden and dramatic change that the aircraft was unable to overcome.  However, it would be only temporary.  

If the airflow direction was actually reversed the control surfaces would likely be blown to a full deflection position one way or the other depending on which side of neutral they were.  

Otherwise, the aircraft would still move forward at 25kts relative to the moving airmass, with the additive effect of the wind giving it 60kts of ground speed.