Hi Emily,
HD Quiz is compatible with thousands of questions per quiz, and there are users who use that many. The only limitation is the power/speed of your server.
I can think of only two possibilities.
1) Since you are only able to see 9 at a time, this means that either another plugin or your theme, is forcing WordPress to only ever return a maximum of 9 results. So the first thing to do is the default WordPress debug steps.
Disable all plugins except HD Quiz and see if the issue persists. If you can now see all of the questions, then we know the issue is caused by another plugin. Reenable each plugin one-by-one until we discover the culprit. If the issue still persists, then switch the theme to a default WordPress theme so we can rule that out as well.
2) The issue could be that you made the 10th question, but that the question is not attached to a quiz (you might have accidentally unchecked it?). Quizzes work kind of like categories for your blog. A quiz is just a category that has questions attached to it. From the main HD Quiz page, select “Bulk Modify Questions”. This will take you to a native WordPress page that will show a list of all questions. Make sure that all of your questions have the quiz name listed in the “quizzes” column.
If neither of the above helps, please contact me at harmonicdesign.ca – I may need to ask you more specific questions that we wouldn’t want to be publically displayed here for security.
