The most common reason for recurring items not being posted is that the item being posted is a duplicate of a previous post. Most social networks do not allow you to post content that is the same as your previous post, or any of your posts within the last 24 hours.
Also, items in your Recurring Posts List will not be posted until 10 minutes after you create a new Recurring Posts List or update its settings. This allows you to tweak the list settings before it takes effect.
Of course, if you believe this is not the case, please create a support ticket so we can look into it.