Cuz the sculk sensor is not yet finished in development it is still not done thats why it's in experimental toggle only
I think they are covered with vines cuz of the lush cave try finding a lush cave near that area and if you it is because when there are azalea trees and lush caves at the bottom vines will be everywhere in the surface
This happened to me to when my cousin is in her house and she is playing and tap the world she is playing in friends option and it says unable to connect to world
Just kindly wait for the next beta