I played that game for years and I never seen any cave looking so weird. It definetly look like the game generation broke in some ways. I'm not sure where the issue can come from, in fact I generated a world with the same seed on the last stable hotfix and the mountain was really different and much more normal, but the inside was already broke in that version.

In fact, I noticed weird behaviours on a lot of newly generated chunks of my survival worlds since last update. I didn't wanted to make a bug report because I thought I probably messed up things enough to have a bit of corruption, which would be possible, but here I recreate the world with the same seed and got the same issue. Something is definetly wrong.

Seed: -5183169847345682987

Coordinate of the place, but I noticed sus-looking place all over new generated chunks: 300 ~ -2570, inside the mountain

EDIT: I'd say there's probably a link with MCPE-189978 since it's also a chunk generation error. I definetly noticed this one too.