Hi, I've implemented research project on using Jackrabbit Oak Lucene, Apache Solr and Elasticsearch in AEM 6.4 on We Retail project. They are all implemented inside the same project so I could measure their results. You can check this project here: https://github.com/tadijam64/search-engines-comparison
Invalid recursion selector value 'searchresultsdata'
Cannot serve request to /content/we-retail/language-masters/en/products.searchresultsdata.json/_jcr_content/root/header/search in org.apache.sling.servlets.get.DefaultGetServlet
I think this is dependency issue where it can not recognise this servlet because of some dependency it uses (probably elasticsearch). Not sure how much sense this has, but I had similar problem in original implementation on 6.4 and it worked only after deploying Elasticsearch as separate bundle. In this case Servlet is completely blocked from processing requests either for Lucene, Solr or Elasticsearch.
By checking out OSGi Components in the Web Console, I've realised there are configurations that this server is depending on that weren't active automatically. By setting them to the default I've managed to solve this issue.