You will see that FTP reports less disk space for a directory than other sources such as the du command or in the cPanel File Manager.
This can occur if the directory has more files than the LimitRecursion setting (default 10,000) in PureFTPD. This causes FTP to stop counting files after reaching the limit. So only the first 10,000 files would be counted by default.
The LimitRecursion setting can be increased by following the steps in our FTP Server Configuration documentation.