The vanes are a supreme bit of kit. As posted earlier, they probably have an AC voltage out, continuously variable, centred on 0, and swinging + or _ . this is derived by a reference AC voltage in, and variable transformer coupling either side of zero - proportional to the vane angle.
Most non-scheduled vane changes are because of heater failure. That constant-ish error 'must' be due to downstream electronics.
Let's get back to the recent thrust of the thread. What other factors added to the vane's error signal and so radically confused two separate crews?