BlinkSteel25

MCPE-121708?
What device and OS are you using?

When the cave air cuts through the lava lakes, it leaves exposed lava source blocks that only start flowing when they receive a block update.
The caves are eating the lava lakes! /s

Overwriting of existing carver generation is a touchy issue. The development team should prioritize preserving existing carver generation. Noise caves should interact with the carver caves without overwriting them.

Suggestion: Noise caves above y=0 should only generate where they don't overwrite a carver cave. Now, this would make noise caves smaller and rarer above y=0, but maybe then noise caves could be larger or more common below y=0? Maybe noise caves could generate more commonly inside the new mountains above a certain y-level? (Because carvers present in 1.16 wouldn't generate above the old surface level anyways.)

Update: As of 1.16.230.56, ores now generate correctly below y=-4! Blobs of Granite, Andesite, Diorite, Dirt, Gravel, and Deepslate also generate at their appropriate y-levels.

However, only Stone and Stone Ores generate below y=-4. Layers below y=-4 should be composed of Deepslate interspersed Deepslate Ores, and Tuff blobs. Tuff blobs also aren't generating from y=0 to y= 16 (because Tuff hasn't been added yet.)

Related to MCPE-121724.

Confirming fixed on my device as of 1.16.230.50

Device: Samsung Galaxy A10e
OS: Android 10

Confirmed for Android: the cave vine body has a noticeably brighter light level than the cave vine head.

Duplicate of MCPE-121868

Duplicate of MCPE-21416

Duplicate of MCPE-122054

affects 1.16.220.52

Duplicate of MCPE-121724.

Duplicate of MCPE-122043.

I realize you're the one who filed both bug reports but they seem like the same bug tbh.

It's because the string ' "count" : 2 ' is missing from the files for these stonecutter recipes.

This is a duplicate of MCPE-121708

By my own research, underground cave carvers do in fact generate. However, they do not generate higher than y = -18.

To reproduce:
1. Generate seed 710079336 with Caves and Cliffs features toggled on
2. Go to coordinates x= 1489, z= -54
3. Run the command from the comment above to create an "air shaft" to y= -64

A cave system should intersect the shaft at around y= -20. You may need to create multiple air shafts to find the cave system.

Edit #1:

Several things I've found.

1. This seems only to affect worlds with Caves and Cliffs Experimental Features enabled.
2. Underground cave carvers generate:
a. in the same pattern as in worlds without Caves and Cliffs enabled, but
b. shifted downwards by 60 blocks
3. Contrary to the OP, in my research this issue also seems to affect underwater cave carvers.

Edit #2:

Just found cave systems that generate well into y= 30 levels. Only, these caves seem to be rarer. It makes sense since normal carver rules are being followed, just shifted down 60 blocks. I'm wondering if anyone else is experiencing "no caves at all" or if it's simply "the caves are generating, but not where they're expected to be".

I added images showing that the borders between normal and placeholder texture "zones" can be irregular. I have no idea if this is useful information or not. It might just show that boundaries between Extreme Hills and other biomes happen to be irregularly-shaped.

Only Gold Ore seems to be affected. Might have something to do with how the new ores (Nether Gold Ore and Gilded Blackstone) are handled? 

you'll probably have to download the free Music DLC from the Marketplace

however, the Marketplace can't be accessed in the 1.16.057 Beta for now

(see MCPE-68973)