Sounds like you have two exact pages, One is a http:// and the other a
https://. This is a good reason for suplimental. Google only wants to display one.
Choose the one you think is more important and get a few links to it, Likely it will come out of suplimental.
Google is making an effort to only display a page once, any other time it sees the same page they turn it into a suplimental. You can deside which one makes it to the main index by providing links to the one you feel if more important. Otherwise be sure you do not have two differrent links pointing to the same page.