"Text rendering mode 3" is invisible text. In a Preflight profile you can search and warn for text that is not embeded but you might not want to be warned if the text is invisible. Your preflight profile seems to check for both this values.
Preflight check in Acrobat. The check will fire if font is not embeded and the text is not invisible.
In a Preflight fix (PDF Tool Box) you can also choose not to embed fonts for invisible text.
