Thanks for your answer.

I found solution on Reddit: fire removes ground fog.
https://steamcommunity.com/sharedfiles/filedetails/?id=2661393729

But fog will come back if you remove campfires
https://steamcommunity.com/sharedfiles/filedetails/?id=2661394596

Good news is torches working too
https://steamcommunity.com/sharedfiles/filedetails/?id=2661394612