AoA vanes can not read accurately on the ground as the airplane doesn't have an angle-of-attack when it isn't moving to measure. The vanes just blow around in the wind and, since the wind on opposite sides of the aircraft will be different, it would be normal for the two vanes to produce significantly different readings on the ground.

As you approach flying speed on takeoff, the relative wind (half of the AoA calculation) becomes greater than the surface wind and the AoA data becomes meaningful.