spring-boot-starter-parent v2.3.1.RELEASE
elasticsearch-rest-high-level-client (version inherited from parent above)

According to spring-boot documentation:

If you have the org.elasticsearch.client:elasticsearch-rest-high-level-client dependency on the classpath, Spring Boot will auto-configure a RestHighLevelClient, which wraps any existing RestClient bean, reusing its HTTP configuration.

In our project, we have a single RestClient bean registered in spring context:

    @Bean
    public RestClient elasticsearchRestClient(ElasticsearchProperties elasticsearchProperties) {
        RestClientBuilder builder = RestClient.builder(
                new HttpHost(elasticsearchProperties.getHost(),
                        elasticsearchProperties.getPort(),
                        elasticsearchProperties.getScheme())
        );

        ElasticsearchCredentials esCredentials = new ElasticsearchCredentials(elasticsearchProperties);
        if (esCredentials.hasCredentials()) {
            builder.setHttpClientConfigCallback(httpClientBuilder -> httpClientBuilder.setDefaultCredentialsProvider(
                    esCredentials.getCredentialsProvider()));
        }

        return builder.build();
    }

Spring actuator health endpoint returns correct response regarding connection to Elasticsearch (uses our parameters etc.).
However when we're trying to use injected RestHighLevelClient to connect (e.g. using client.cluster().health(new ClusterHealthRequest(), RequestOptions.DEFAULT); it connects using default parameters from spring-boot.