Tier info is not returned by the api yet. Tier info importing for posts will be possible after api has that feature.
If new posts are not coming in, your site may have lost connection to Patreon. You can employ below guide to force it to refresh:
If plugin is double-importing posts, there is a situation at your WP installation - plugin knows which posts it imported. So it shouldnt happen.
But, if you already had some posts posted manually at WP before, and you re-imported those posts for the first time from Patreon, then double posting can happen if the post titles dont match each other.
You can delete the double posts from post manager normally, like how you delete any post.