Disk 1 has 1.4T of data on it, and the cache has 56G of data on it (all the appdata share).
This would be my best guess as to the problems if you used the Cleanup Appdata plugin.In the case of a massively misconfigured docker app being installed at one point, then the plugin will dutifully want to delete what you've set the /config mapping to. Which is why it has the double confirmation, folder list, and big banner warning.