You may find that learners' responses are missing from Articulate Online reports for courses that were published with Articulate Presenter '13. (Scores and statuses are correct, but the actual responses aren't showing in reports.)
This issue was corrected in Update 3 for Presenter. To take advantage of the new features and fixes, download and install the latest version from the link in your product confirmation email or get it here, then republish your project to Articulate Online. This won't fix the missing responses for learners who have already taken the course, but it'll prevent the issue from happening again.