Lush caves sometimes generate without any cave vines, this makes them look pretty dark and it goes against the theme of the biome + it's pretty ugly 
This also happens when the entire cave is located within a lush cave biome so it's not caused by 3d biome ending
Expected behaviour: Lush caves would always generate with cave vines 

Observed behaviour: Sometimes lush caves generate only on the ground without any vegetation hanging from the ceiling or the other way around or without any vegetation at all

(note this might be hard to reproduce because of MC-219200)

How to reproduce 21w41a:
Seed: -9235201
/execute in minecraft:overworld run tp @s 174.94 -16.91 -443.44 -1262.83 -2.10

How to reproduce in 1.18 pre4+:
Seed: 47636
Coordinates: 3068 -48 -1112, 3006 -34 -1211, 2951 -53 -1214, -4801 -24 -758