Stone walls created from a version earlier than 18w10a become invisible in current snapshot versions. They also become walk through-able. The image shown is an instance of the glitch which is making the torches appear to float in midair (torches are on stone walls). To fix the stone walls in-game, you have to place another section NEXT to the stone walls then all or most reappear. I upgraded to an earlier snapshot, the one before 18w10a.