A likely cause is exposure compensation being set away from 0. On the GX80, exposure compensation affects Auto and many semi-auto modes, and if it has been bumped to a positive value the camera will intentionally overexpose, making images look very bright and washed out. White balance won’t fix exposure, and changing aperture/ISO may not help much if the camera is still compensating exposure automatically.

First, check the exposure compensation setting and reset it to 0. If that solves it, the lens is probably fine. If needed, also try a full reset of shooting settings and test again with both lenses in the same mode.