Because Knowledge v3 does not use ACLs to restrict access, knowledge search includes results that are restricted via ACLs for the current user.
The article appears in search results but you cannot view the full article.
Do not use ACLs to restrict articles when using Knowledge v3. In v3, security is handled strictly by user criteria:
If you need to prevent certain users from seeing knowledge articles, move those articles to a separate knowledge base with more strict user criteria.
For more information, see: KB0550924: Understanding User Criteria and ACLs in Knowledge v3.