Hi,
Please note that WP RSS Aggregator will only import unique items, regardless of any settings. An item is considered to be unique if no item with it's permalink exists anywhere in the system. The items' permalink in the feed is defined by the <link> tag, or the <guid> tag if it's isPermaLink attribute is set to true. Once imported, the permalink is stored in the wprss_item_permalink custom field of the resulting posts. Hence, if, for example, you have a post with the wprss_item_permalink set to this URL, WP RSS Aggregator will not import another item which has that permalink.
This behaviour is desired almost universally, and I believe that this is what is going on in your setup. If this is so, it means that the system is working well and as expected. Please consider changing your review and rating.