Good news! Worklogs - Time Tracking and Reports team has just released a new version, and since you use Jira Server you can decide to upgrade at any time! All that is needed is a click of a button in the Apps management screen on your instance!
New features
Export of totals and sub totals to Excel file, configurable in the export modal.
Detailed documentation: https://soldevelo.atlassian.net/l/cp/J1L6eXHM.Worklogs sharing URL now also includes totals and sub totals configuration.
Improvements
In the gadget, the old export menu is replaced with the new export modal. Now export works in the same both in the gadget and on the main Worklogs page.