I guess you're using a 7.x version?
May be this explains?
By default, Elasticsearch periodically refreshes indices every second, but only on indices that have received one search request or more in the last 30 seconds. You can change this default interval using the
index.refresh_intervalsetting.
And
How often to perform a refresh operation, which makes recent changes to the index visible to search. Defaults to
1s. Can be set to-1to disable refresh. If this setting is not explicitly set, shards that haven’t seen search traffic for at leastindex.search.idle.afterseconds will not receive background refreshes until they receive a search request. Searches that hit an idle shard where a refresh is pending will wait for the next background refresh (within1s). This behavior aims to automatically optimize bulk indexing in the default case when no searches are performed. In order to opt out of this behavior an explicit value of1sshould set as the refresh interval.
I'm running in AWS ES
BTW did you look at Cloud by Elastic, also available if needed from AWS Marketplace ?
Cloud by elastic is one way to have access to all features, all managed by us. Think about what is there yet like Security, Monitoring, Reporting, SQL, Canvas, Maps UI, Alerting and built-in solutions named Observability, Security, Enterprise Search and what is coming next 
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