i will get this warning when light is really low, such as pre-dawn or after sunset.
the air2s will still perform well in that light, just be aware that obstacle avoidance is handicapped. and use a flashlight to illuminate your take-off and landing spot.
you can check to see if anything is blocking your aircraft's 'eyes', aka vision sensors.
if you get this warning in full daylight, with nothing blocking, you might have a hardware problem.