Symptoms
When migrating from SharePoint 2016, pinned site pages are not preserved.
Details
A pinned site page is a site page that a user is currently following (can be found in the user's profile) and that has been pinned so it stays on top of the list of followed site pages. The ShareGate migration tool does not currently migrate informations contained in user profiles. Since pinned pages are in the profile of the user, it will not be preserved.