Plesk is not calculating reseller bandwidth usage correctly. It displays less than the actual usage or 0 on the reseller's page.
Home > Reseller > <RESELLERNAME> > Resources includes only reseller's own subscriptions without considering traffic from subscriptions of the reseller's customers. This issue has been considered as software issue #PPPM-2618 and was fixed in Plesk 12.0, microupdate #39 .
Apply latest Plesk microupdates .
Custom fix available before microupdate #39:
Download the custom fix from attachment .
Back up the original file and replace with the fixed version: