This started a few days ago. Basically the console is filled with same error message about an MP3 file. So many errors that console is unusable to run commands. RAM memory for CSS keeps increasing until Windows kills it, so can only play on server for 3-5 mins until CSS crashes.
Just to be sure it is not client-side. Just verify CSS game cache and try again. Tutorial link if u don't know https://inxile.zendesk.com/hc/en-us/articles/115004662908-Verify-game-cache-files-Steam-
Not a server sided issue or problem. I'm assuming there was an issue when you originally connected to the server when it was downloading the welcome.mp3, so I'd delete that file and re-join.
In future if you get an message such as this or missing map etc. Then delete the map that's missing because there would of been an error during download so the file is partially downloaded but not working correctly, so deleting it will let the server download the map/file for you.