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.