You probably get this message because you don’t have enough posts to fill both cover area and main post listing below.
Disable “Make cover posts unique” option
Inside Theme options -> Category template you will find the option which prevents posts to appear twice on the same page. If this option is enabled, posts in cover area will be automatically excluded from the main listing below and that’s probably the reason for getting the message.
Disable “Cover area” entirely
You can also turn off cover area entirely for this category until you have more posts to display, or, lower the number of posts in cover area.