Affects Version/s: Minecraft 18w10d
Fix Version/s: None
Environment:Minecraft 1.13 snapshot 18w10d.
Only tested on Jungle Biome.
In minecraft snapshot 18w10d, Jungles generate different than before. In the first screenshot you can see that the jungle is way more dense in trees than in earlier versions. Vines also generate underground, creating air pockets in stone, which you can see in the second screenshot.
I haven't checked if this is also the case in other biomes, but in the Jungle it's easily seen.
I hope this gets fixed in an upcoming snapshot.