Single Player Lag Spikes & Biomes changing in generated chunks

While using the Caves & Cliffs preview datapack, after several minutes of gameplay I experience frequent lag spikes. This occurs when moving any distance less than one chunk.

Today I started a Large Biomes world and began building in a Savannah. After briefly leaving the Savannah biome and returning, the biome had changed to an ocean biome. All the original terrain remained, but now the grass and leaf colors had changed.