The import algorithm will not import keywords already in the ad group, especially if you create negative and import rules with the same criteria.
For example, the Discovery strategic objectives are preset to add search terms with sales as new keywords, negating them in the Phrase and Broad ad groups.
For example, when setting up the Fully Managed Campaign, we add a list of keywords, such as "jump rope."
When "jump rope" generated sales, the negative rule executes to negate them in the Phrase and Broad ads.
The change logs show the negative rule negating the keywords, but the import rules do not add the keywords because they already exist.