Since this commit, RelatedArticles use the hardcoded /w/api.php as the default API URL for CirrusSearch.

This is not an issue for WMF wikis because they use /w as script path. However, when the wiki is not using the same script path, the API call would result in a 404 and the RA cards won't be rendered.

For the best practice, the default for RelatedArticlesUseCirrusSearchApiUrl should use script path to api.php instead of just hardcoding /w.