Are you sure all the Unobtrusive libraries are loaded? An @Ajax.ActionLink
generates a standard anchor tag. If the JavaScript libraries aren't loaded to handle the click event, you'll get the GET request you see in Fiddler.
Check to see if the jquery.unobtrusive-ajax.js
script is included in a bundle that is referenced from your layout page or that you're explicitly loading it on specific pages in a scripts region.