Let me give you some more information, because I think you are forgetting some of advanced options of your plugin and wordpress.
I setup a facebook autopost. In advanced, I checked the option to republish automatically and checked “Loop it. Reset and Start from the begining”. After some months, the plugin will start to republish some old posts.
Now, what is a private post ?
Private content is published only for your eyes, or the eyes of only those with authorization permission levels to see private content. Normal users and visitors will not be aware of private content. It will not appear in the article lists. If a visitor were to guess the URL for your private post, they would still not be able to see your content. You will only see the private content when you are logged into your WordPress blog.
You can read more in Codex:
https://codex.wordpress.org/Content_Visibility#Private_Content
More here:
Private: Viewable only to WordPress users at Administrator level. (private)
https://codex.wordpress.org/Post_Status
So what exactly are you asking us to do?? At the time you make post private it’s already autoposted.How SNAP can un-autopost it?
Who is asking for un-autopost it ? I am asking to you make the plugin check if the next post to be (re)published is marked PRIVATE before the plugin (re)autopost it. If is Private, then try the next post in queue.
Why SNAP will use a published post marked like private ? It is irrelevant if the post has been republished before or not. The post is Private now, so it must not be republished by your plugin. Remember the option: “Loop it. Reset and Start from the begining”
1. You make new post and publish it on your site for everybody to see.
OK
2. SNAP autoposts it to all your social networks.
OK
3. You make post private
.
OK
4. If the option “Loop it. Reset and Start from the begining” is checked, SNAP will check the actual status of the next post to be republished. If it is Published AND NOT PRIVATE, then republish (when it is your turn to be republished). But if the post is marked PRIVATE, dont republish it, try the next post in queue.