The bug

Many panda sounds that are defined in the panda's sound definitions do not exist in the vanilla files. As a result, when these sounds attempt to play, it just plays nothing instead. So pandas are just silent like 50% more often than they should be.
The game should produce a content log warning when a sound event references a file that does not exist.

The list

• sounds/mob/panda/nosebreath1
• sounds/mob/panda/nosebreath2
• sounds/mob/panda/nosebreath3
• sounds/mob/panda/pant1
• sounds/mob/panda/pant2

They are used in these sound events:

• mob.panda_baby.idle
• mob.panda.idle
• mob.panda.idle.aggressive