Issue
When opening any knowledge article in the new Knowledge Portal (/km), the article is not displayed and you receive an "Article not found" message.
Cause
The Portal Page "Knowledge Article View" [kb_article_view] has been customized and is not using the OOB widget "Knowledge Article Content" [kb-article-content].
Portal Page "Knowledge Article View" [kb_article_view]
https://instance_name.service-now.com/nav_to.do?uri=sp_page.do?sys_id=a60dcc050be432004ce28ffe15673a54
Widget "Knowledge Article Content" [kb-article-content]
https://instance_name.service-now.com/nav_to.do?uri=sp_widget.do?sys_id=a47ea1cb0b9432004ce28ffe15673a5b
Resolution
Revert to using the OOB widget "Knowledge Article Content" [kb-article-content] in Portal Page "Knowledge Article View" [kb_article_view]