After playing for a short while, all other sounds that are not a part of the mod will turn off. No subtitles appear either.
The sound turns back on if I mute and then unmute the master sound setting.

This is very irritating and I cannot find a fix anywhere.

I believe it turns off other sounds if too many occur at the same time, but I am unsure.

This happens consistently, over the past 2 days since installing.

There are an issue with the config. Go to /cmdclientconfig -> AmbientSounds and reset the values for fadeVolume and fadePitch. Maybe you are also using an outdated version of CreativeCore? Would also be good to know what minecraft version you are using. You can also use the command /ambient-debug to see which sounds are currently playing. Maybe that helps to pin point the issue further if my first suggestion does not fix it.

Also I'm very sorry for responding sooo late ... I'm have been quite busy.

I will close this issue due to inactivity. If this issue persists just report it back here.