The Bring Forward Annotations icon is not appearing on a document in Vault as expected for a user.
If the Bring Forward Annotations icon is not appearing on the document, it is either because there are no valid annotations on the document that can be brought forward to the current version, or it is because the affected user does not have the correct permissions to bring forward the annotations.
The user, who experiences this issue, needs to be given the proper permissions to bring forward annotations. Or, valid annotations have to exist on the previous versions of a document for the icon to appear.
The permissions needed to bring forward annotations are listed in the Help Documentation page linked in the Related Documentation section.
Vault Annotations Documentation: How to Bring Forward Annotations