I've been playing in this world since long before Caves and Cliffs Part 2 released without messing with any beta features on this world. Just recently I discovered a Chunk didn't fully get updated. While the world did get extended below the bedrock, the bedrock prior to Caves and Cliffs Part 2 wasn't converted to Deepslate. Attached are pictures of the afflicted chunk. Feel free to use your infinite powers to take a copy of my realm or whatever and check it out for yourself.