Hi,
Any one help me regarding how to know in elastic the exact time when connectivity was lost and restored to elastic, even if logs are backfilled upon reconnection
Are you referring to connectivity between Elasticsearch nodes or between clients and the cluster? If it is between Elasticsearch nodes you should be able to see it in the Elasticsearch logs. If it is between clients and the Elasticsearch cluster you likely need to look at the logs on the client side (may or may not be reported).
If you want to track ingest delays going forward you may want to configure an ingest pipeline to add the ingest timestamp to the event. Based on this you can then calculate delay and see volumes ingested over time.