The keyword doesn't appear in the patents of the search results on PS

The reason for this situation may be the result of the setting of "Stemming" which enables users to include other forms of a term, such as verb and verb+ing, in the search results. Therefore, there can be patents which have a verb or other forms of the keyword but do not have the exact keyword in the patents. If you want PS to show the exact term only, simply deselect the "Stemming" feature in the "Settings" as below image.