Not enough space, but Finder says otherwise

This is a very frustrating thing for me and I hope someone can give me a hand here.

Main disk: 1TB

Backup disk 1.5TB

I create backups using CCC (Carbon Copy Cloner), but it keeps saying the destination is full (1.5TB). How is that possible if I'm creating a clone of my main disk which is only 1TB?

Also, when I go to my backup disk using Finder and I calculate all folders' sizes, it goes up to around 1TB or so, not 1.5TB. Even the free space on that main disk is 40GB, so I'm not even using its full capacity of 1TB.

When going to Disk Utility, I get the same issue which is, it says I only have a few MB free. Where the heck are the extra 500GB?

Even if CCC creates snapshots (which are not even showing on my snapshots list), I don't think it would use 500GB.

Can anyone clarify what's causing this?

Here are some images: