[Galaxy S6/S6 EDGE]Is it faulty that the camera lens appears off center and moving?

Your device is not faulty.

The Galaxy S6 series front facing camera supports “OIS” (Optical Image Stabilizer)

feature to minimize shaking when shooting pictures, previewing, recording video, and

the exposure time automatically adjusts to take sharp pictures in a dark environment.

For this feature, Galaxy S6 series front facing camera has been designed to enable the

Lens unit to move up and down.

However when the OIS feature is deactivated e.g. while camera is turned off the camera

lens may appear to have located itself slightly off centre after the camera has been used.

But, if you activate the camera, OIS feature will also work and camera lens will locate on

center.