Along the the orange circles to the right with a number and arrow to the side. I never saw this in the display before with earlier versions of Acrobat, and I'm not finding them at all helpful. There is no information about what they are, how to use them, or how to clear them. What is the story with this feature?
Sorry for the delayed response and inconvenience caused. The orange circle with a number and arrow represents that you have an unread comment from the user. Once you click on the comment from the user, the orange circle will disappear.
The number represents that you have 1 or 2 unread comments from the user. This feature is included in the Acrobat DC versions.
For more information, you can refer to Participating in a PDF review, Adobe Acrobat and https://helpx.adobe.com/acrobat/using/starting-pdf-review.html
Feel free to update this discussion for any further assistance.