Symptom
You migrate a task list and notice that the titles or your list items are replaced by the item ID at the destination.
Details
Your list items are migrated correctly. The issue is that Microsoft 365 displays the ID instead of the title when using the Modern Experience in your task list.
You can change the List experience of your list from Modern experience to Classic experience with these steps:
In ShareGate Migrate, go to Explore.
Connect to your Microsoft 365 site collection or tenant if it is not already connected.
Navigate to the site that contains the affected list(s).
Select the list.
In the Quick actions menu at the right, scroll down and find List experience.
Click on Modern experience and change it to Classic experience.
The titles should be back when you return to the list in SharePoint.