What it says on the tin. The Night Vision trait, along with High Night Vision, Full Night Vision, does not work. (Probably along with any other night vision traits.) The Implanted Night Vision bionic seems to work fine, though.
Have you tried turning it on from the [ menu? It was changed recently to an active mutation, since it being always-on made it impossible to see external light sources.
Oh, I feel stupid now. Thanks! 
There’s no need to feel stupid. It used to work one way, and it got changed recently. If anything, it’s our fault for changing it!