I have posted about the same issue in the past. i get a notice that an item did not post due to "failure".
I used to immediately repost the item that failed. After receiving duplicate notices, I now check the active listings because at least half of the time the notice is erroneous and the item did in fact post.
I don't think this happens when the notice suggest api failure. in those instances (and trust me I check) the item actually did not post.
The issues I have experiences is when the notification describes the failure to post as "failure".
I have had serious repercussions to duplicates violations and I double check everything. I even audit all my listings by using the active listings folder and filing by title, every day and sometimes twice a day.