I was flying through my world and I noticed this very long strip of darkness. It seemed to be only one chunk wide, though it stretched out very far. It didn't go indefinitely, but it was further than my render distance.

Placing a block in the strip wouldn't get rid of the darkness and a torch would light up, but would go back to darkness upon removal. Setting the time to day didn't fix it either.

Don't believe I've seen any other posts with this bug.