Project Zomboid
Ultimate Music Pack
This pack alone doesn't work in MP
Although I do have 356 mods in my collection, however all your other mods do work! I saw someone was also having issues with MP last year.

I've tried:
  • Uninstalling & Reinstalling
  • Turning off the mod (Which it worked when disabled)

I'll try loading a MP server soon with JUST this mod.

Here is my mod list in case you need to check it!
https://steamproxy.com/sharedfiles/filedetails/?id=2580742419