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
is this still an issue?