The issue here is that the user's permalinks are not working after migrating their site resulting in a 404.
Solution:
It would appear that your permalinks need to be reset. Can you go to your backend and click on Settings -> Permalink and set the permalinks to default.
Once you've done this check again on the frontend to see if the pages will now load with the default permalinks. If they do go back to Settings -> Permalink and then change the permalink settings back to Postname.
