Re: What is
To learn what it does, check page 39 of the manual (1.8 version)
When FPV(First Person Vision) mode is
enabled, gimbal roll motion will synchronize
with the aircraft for a real time FPV experience.
When FPV mode is disabled, the gimbal will
stabilize across three axes for smooth aerial [20] creativity. This mode is only available on the
Phantom 2 Vision+.
Don't know why it isn't working for you.