How does this Sort by "Relevance" work, or what is the logic behind its algorithm?

Summary:

How does this Sort by "Relevance" work, or what is the logic behind its algorithm? We have created two different agreements for the same item, and when we are searching for it on the shopping page, it always shows the item in the same sequence as shown in the below screenshot. Even if the last updated date changes, the result sequence doesn't change.

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