I have reviewed the linked image of your feed. I may need a bit more clarification as to what you are referring to.
If it is the red line that appears between the posts then this is a result of your current plugin settings which control the appearance of the line. You can find the settings by going to your WordPress Dashboard – Facebook Feed – Customize – Post Layout – Post Style section.
If it is something else then please provide a bit more detail and also a link to the page where the feed is installed as it is quite possible another site component is affecting the appearance. You can see the feed from the same source is working correctly in our demo here.
