For testing Session Relevance queries, I’d recommend using the Web Reports QNA page as described at QNA in Web Reports
URL: https://<reportsserver>/webreports?page=QNA
I don’t see a problem with the query itself and it returns correct results for me, but try it out in the QNA page to be sure in your deployment. Once you are certain the query gets correct results, I’d check whether whatever tool you’re running to send the query through the API is properly URL-encoding the query (i.e. replacing " with %22, spaces with %20, etc.) Often the URL-encoding is done automatically, but it depends on how you’re sending the query.