After I tested and removed MODX extra Ticket, there is still a non-working menu entry ticket_menu_desc in the Extras menu. How could I remove it? Somehow, Ticket's uninstallation script didn't remove everything needed. The error log is now flooded because Ticket files don't exists anymore.
Go to Menus (top right menu gear icon -> Menus, path is yourwebsite.com/manager/?a=system/action), find your Ticket extra point in left menu tree, right-click on it and select "Delete Menu item".