How to fix

• Option #1: 
  • "Content" pane:
    • View > Show/Hide > Navigation Panes > Content > right click on the contents that you want mark as an artifact and select "Create Artifact"
• Option #2:
  •  "Reading Order" pane:
    • Tools > Accessibility > Reading order > Show reading order > Review the reading order (You can review your content by selecting "Page content order" or by "Structure types") > select the content that requires tagging > Chose the type of tag > OK
• Option #3:
  • "Tags" pane:
    • View > Show/Hide > Navigation Panes > Tags > Use the tag tree displayed in the "Tags" pane, review your content and tag them as necessary

Screenshots

Please refer to screenshots in the Tagged PDF content section.