It's the old lighting texture/rendering bug that has been bought to the developers attention multiple times yet they seem reluctant to do anything about it. You'll notice at the same time that your shadows are missing and the day seems really gloomy with dodgy contrast making it hard to see if you look above the horizon anywhere you can see sky. A friend could be playing with you, standing beside you and be experiencing a beautiful sunny day.

Usually happens after a server restart but doesn't affect everyone.

You can generally fix it for yourself by shutting game down and restarting it and then logging back in to the server but it will likely happen again at next server restart.

It would be a major turnoff if i would get to be stolen because of such a horrible bug. As a solo player, building structures to see them raided while offline is not an option so i thought the safest way was to set my stash in water. Im very disappointed to discover its not safe at all.