When feature option "Assignment Enhancements - Student" is enabled, if a student submits their work via Google apps, when you go to speedgrader, the submissions will not have a preview. When feature option "Assignment Enhancements - Student" is disabled submissions will show a preview in speedgrader.
Instead, supported file types should show a preview in speedgrader.
Steps to Reproduce
Create a course and enable feature option "Assignment Enhancements - Student" enabled.
Create an assignment and set the submission type to file upload and publish the assignment.
Masquerade as a student and go to the assignment and select more options and choose Google Apps and selected a supported file which can be rendered in DocViewer.
Masquerade as a teacher and go to speedgrader, and you will see that the submission has no preview.