This was solved. With the best current understanding, the problem was incorrect usage of Python Elasticsearch library combined with incorrectly configured nginx reverse proxy. This caused the Elasticsearch REST request from Python to be routed to Kibana. Kibana actually responses but it does not process the query body (or the body was not received correctly through nginx).
For me, using location like below for Elasticsearch in nginx and the '$is_args$args' was needed to pass the query parameters like the scroll_id.
location ~ /elastic(/|$)(.*) {
set $elasticsearch_servers elasticsearch;
proxy_pass http://$elasticsearch_servers:9200/$2$is_args$args;
}
The second issue was incorrect usage of Elasticsearch Python library where the url_prefix was not used correctly. I tried to use this in the host setting like 'Elasticsearch(['http://10.100.100.100:8080/elastic'])' which lead to default location in nginx that was Kibana.
>>> from elasticsearch import Elasticsearch
>>> elastic = Elasticsearch(['http://10.133.196.101:8080'], url_prefix='elastic')