In DirectAdmin there is a feature that calculates the disk usage in File Manager. Sometimes, it can slow down the File Manager and need to be disabled. To disable it, you may SSH to the server and,
# vi /usr/local/DirectAdmin/conf/DirectAdmin.conf
Find and change the value of this directive to 0 (zero), if the directive does not exist, you can manually add it.
Please take note that by disabling this feature, this will replace the usual 4.0k you see for all directories. It will also replace the directories true size (hidden in the form, used for sorting. This also affects the API for the filemanger).