In 2018 WT redesigned the Sound Engine. A side effect was that all current Sound mods were no longer functioning (ie EPIC Thunder).
In Sep 2019 WT released the tools to create mods for the new engine:
https://warthunder.com/en/news/6372-...war-thunder-en
Now, WTLive added a "Sound" tab
https://live.warthunder.com/feed/sounds/
On top of that, but there are a couple of mods out. I have loaded the "Fury Thunder" mod (previoulsy known as "Standart sound mod" on the main mod page) and it sounds nice.
https://live.warthunder.com/post/883037/ru/