I just tested on my local setup and more than 10 posts are randomized. We don’t limit the number of the randomizer posts. I’m not sure why it’s happening for you. A few questions to debug this further:
a) Are you using date range feature for randomizer posts?
b) Are you using randomizer categories?
c) Are you using both text and images for content?
d) Would it be possible to take a look at your setup? We can also provide you with a test site to help us replicate this issue.