I have gone thru Minecraft forums and this seems to be known issue. As I operate Minecraft 1.7.2 server that had great community, after this issue came into the account, I have lost over than 90% of players.
So far is seems that folder .minecraft/assets/virtual is not being created by latest MCL (old legacy launcher does it just fine). Idk the way how to force MCL to do so (not implemented?). The folder contains all sounds as needed by version 1.7.2 - virtual folder structure described in file .minecraft/assets/indexes and also refered in .json file inside ./versions/1.7.2 folder. I have tested some older versions like 1.6.4 and it is the same. Version 1.7.3+ does not use virtual structure anymore so runs w/o any issue.
I could prepare some unofficial fix (patch) that installs missing virtual directory but imho it will not comply the EULA, could I receive some sort of approval from Mojang/Microsoft side? My goal is to propose legacy community some kind of easy fix.
Thanks in advance.