Friday the LinkedIn authentication expired, so today I re-authenticated the plug-in.
However, when posting to LI, it responds with an 409 error:
com.linkedin.restli.client.RestLiResponseException: Response status 409, serviceErrorMessage: com.linkedin.publishing.util.common.ResponseException: Content is a duplicate of urn:li:share:6541245998692356097 - 409
According to the error, LinkedIn has detected the content as duplicated and it doesn't accept it. The recommendation is avoiding publishing duplicated content.
If you are sure that the post was only posted once, then a connection problem could be the cause. By default, if there's a connection problem, AutoTweet and Joocial retry the publishing. So, if the original post was accepted (but the connection returns an error), then the post is reposted. If the posts are being posted, you can disable the retries (Options / Advanced / Automatic resend attempts)