[Galaxy S8/S8+]Light appears and spreads on a light source after taking picture?

The phenomenon that appears on your camera is not faulty.

It’s normal flare phenomenon and it can occur when shooting under backlight that sun/light is located
close to screen frame or fingerprint/foreign matter gets on the lens.

Especially, when you take shoot of objects around bright lights, you can easily find it.

At that time, please specify where sun is not so close to the screen or check again once you have
removed the foreign material on lens(As foreign matter can remain according wiping method, please
wipe the lens in a circle around to remove the foreign material completely) It may differ slightly by lens
specification and foreign matter on lens.