After the first data sync has run successfully, order sync from Magento1 can be deactivated as the sales-tracking from the extension takes over.
To deactivate order sync, go into your Magento1 backend, choose SYSTEM in the menu bar and press CONFIGURATION:
Choose the main site (the site you're attempting to affect) under CURRENT CONFIGURATION SCOPE:
Then click on SETTINGS under the CLERK tab in the left side bar and then change the field next to DISABLE ORDER SYNCHRONIZATION from NO to YES. Press SAVE CONFIG to make the changes take effect immediately: