When performing a search query that displays the Site Template column in the results, sites that were created using custom site templates return the wrong value.
When looking at the properties of a site created using a custom site template, the Site Template property returns the wrong value.
A SharePoint site created with a custom site template doesn't hold a reference on the custom site template once the site's creation is completed. SharePoint only keeps a reference on the out-of-the-box site template (or WSP deployed site templates). As such, the ShareGate migration tool cannot retrieve the name of the actual custom site template that was used. Instead, the ShareGate migration tool will display the name of the out-of-the-box site template upon which the custom site template is built.