Hello. For some reason, Wither Storm music wasn't playing. I had my master volume and music to 100%, but it still didn't play music. What happened?

Please fill out the template.

Btw check the Client Config.
Are options 'Play Wither Storm theme' and 'Play Symbiont theme enabled?

In the client config (Options > Purple "W" > Client) enable "Play Wither Storm Theme" or "Play Boss Themes" (depends on the version of the mod, which you didn't specify by not filling out the template)