KeywordText not searching Incident Subject

Summary

How do I get the KeywordText search to search the Incident Subject?

Content

The KeywordText search is not consistent.

For example, If I have two incidents with ROG in the incident subject - it returns only one.

If I have one incident with LTO in the subject it doesn't return it at all.

If I have 13 incidents with BaRA in the subject it returns all of them.

If I have many many incidents with "Test" in the incident subject it returns only 30 of them, and some of them don't have Test in the subject but they do in other data in the incident.