It could be that your story is set to private or has specific settings that don't allow reposting. Also, the platform might have certain guidelines in place that others need to follow to repost content.
It's hard to say exactly. It might be that your story doesn't have the share option enabled, or maybe it doesn't meet the community guidelines of the platform where it's posted.
It depends on the platform. Some platforms are more prone to such issues. For example, if they are constantly updating their sharing features, there might be some teething problems. Also, if a lot of users have similar complaints, then it could be a common problem related to a recent update or a widespread bug. However, if it's just you, it might be something specific to your account settings or content.
Well, it could be that the platform you're using has some sort of bug. You can try updating the app to the latest version. Also, make sure that your account is in good standing, not restricted or flagged for any reason. If it's a website - check for any script errors or problems with the code related to sharing functionality. Sometimes, it could also be a regional or network - related issue, so try accessing from a different network if possible.