I am running 7.5.2.
I am using NEST library for C#. if you see function I posted in my previous topic Strange issue with Elasticsearch while bulk indexing it has eventhandlers for onNext, onError, onCompleted. After I successfully bulk index few times and this behaviour starts, neither of those events gets triggered, no exception gets thrown and code execution continues. Kibana stops working because elasticsearch response time gets above 30000ms or some similar number. On top of that, before I started to set refresh_interval to -1 once I'd request http://domain:9200/index/_count it would load my request after several minutes, now it loads instantly but kibana is still not working. That's behaviour I call unresponsive. If there is different term for it my apologies English is not my primary language.
p.s what is your server's storage configuration if you dont mind sharing?