Unable to detect the Elasticsearch version running on the cluster:

We are getting this error after migration in HS 6. We are getting this error for only default spring profile.
(It was working fine for default profile in HS 5) . Any reason??

Hibernate Search encountered failures during bootstrap. Failures: default backend: failures: - HSEARCH400080: Unable to detect the Elasticsearch version running on the cluster: HSEARCH400007: Elasticsearch request failed: Connection refused Request: GET with parameters {}\nResponse: (no response)

We wondered we have not configured elastic search endpoint anywhere in the application and still able to connect with elastic search server to fetch data in HS 5.