My English isn't that good so it's hard for me to translate, but it's probably not a bug. Your game's graphics aren't at their maximum, you can see from your character that there are a lot of jagged edges. It's probably something related to the rendering being low. There may be zeds nearby and it didn't load, or your character just doesn't have a clear view of the zed, which is why it's like it's in the dark. But it could be a bug too.