While generating a new 9.0.11 map for my server, I noticed that there were very weird biomes and sharp chunk borders generated around my world (Video link below). Upon closer inspecting, I learned that they were Drowned/Ultra Space biomes spawning in the overworld, and causing horrendous terrain.
I was told to clarify in this bug report that the world was
1.) Generated using BYG
2.) Generated in version 9.0.11
3.) Did not exist prior to 9.0.11
I am not sure how to replicate it, as it seemed the chunk loading was random, but it was the first time I encountered this and am concerned if it'll happen all around the world.
Video:
https://youtu.be/2JdRPMF8_XU