I am on the latest version of WordPress, JetPack and your Plugin. I am also using the brand new Twenty Fourteen theme from WordPress.
There is an issue where on some of my posts, I can't display more than 1 ad.
I only have 2 ads. 1 is the sidebar ad which I set to prioritize and the second is 1 block ad that I place at the bottom of the page (only in posts). I am squelching block ads on the homepage.
On certain posts, if set to Widget/Sidebar priority, the sidebar ad will show but the block ad at the bottom of my post will not show. If I uncheck prioritize the widget/sidebar then on that same post the block ad will show at the bottom and the sidebar ad will vanish.
So it seems like on some posts I can't show more than two ads. On other posts I CAN show more than two ads.
I think there may be some pattern based on post length. I think if my post is quite long and contains numerous pictures I am only getting one add.
I think this has to be a incompatablility issue with another plugin. Maybe even JetPack. But I haven't been able to narrow it down.