Details
In SharePoint Designer, you can hide a list or library by checking Hide from browser in the General Settings.
When a list or library is hidden, ShareGate cannot read and migrate it.
Note: System lists and libraries (Access Requests, Master Page Library, etc.) could also be hidden in ShareGate Migrate.
To find how to reveal system lists, see Hidden items.
Solution
You must unhide any hidden list or library before you run your migration. This can be done from SharePoint Designer or using PowerShell. Once the list or library is no longer hidden, perform your migration.
Note: Site collection admin permissions are recommended so you can see hidden lists and libraries in SharePoint Designer.