The OOB client script Custom Knowledge Search on the [hr_case] table adds a specific condition in [kb_knowledge].[topic], line 8:

url += "&sysparm_query=topic=Human Resources";

This causes knowledge base articles not to be retrieved for [hr_case] records when OOB knowledge content is modified by topic or category.

OOB knowledge topics are:

• Applications
• Human Resources
• Policies

Remove line 8 from the client script:

url += "&sysparm_query=topic=Human Resources";