Cannot load the Elasticsearch cluster for your index

#10 don't work for me, the page enter in infinite loop.

In my case the problem come using configuration split, this module settings was moved from general configuration folder to the a split folder. Importing configuration this module become unconfigured, and lock all the site.

#3 worked for me, first you need to add a cluster on admin/config/search/elasticsearch-connector/cluster/add then it will appear on the admin page.