Files that have not been checked-in will not be visible. The ShareGate migration tool will only be able to see or handle the last checked in version of the file. It is recommended that you always check-in files.
For more information on this, please see Changes that were made since the last checked version will be lost during the migration
Tip: You can download a report to find out if files have never been checked in. Download the Documents never checked in report from our Pre-built reports list.