When the cave ambience starts playing, it fades out very fast after just walking a few blocks, a similar issue was fixed for the goat horn recently, see: (MCPE-153254)

Steps to Reproduce:
1. Go to a cave (aparently simply going to a dark spot can work too...)
2. Put the ambience volume on 100%
3. Keep exploring until it plays

Observed Results:
The cave ambience plays on a very low range, which means the volume will drop down very fast if you are walking (it's very noticeable and the only way to hear it properly is if you are on the exact spot it started playing, which is very, very rare)

Expected Results:
The cave ambience can be heard from a bigger distance