The content of the slides is not lost. The loss of some of the slide titles in large presentations is currently under investigation.
Steps to reproduce:
1. Create a Powerpoint file with a large number of titled slides in it (300 or more slides).
2. Start a SmartCloud Meeting.
3. Publish the slide you created in Step 1.
4. After the file uploads and is converted, select the Next button from the toolbar and you will see the list of slide's in the presentation. Scroll down to the end and you should see the slide title change to “undefined” as seen below.