Hi @pawann  I have gone through past support tickets and am unable to find any reference to hotfixes existing to remedy this particular symptom, even in 8.4.

I found a support article which shows workarounds when Work indexes display as unavailable on search landing page. 

For earlier releases this was also documented: Batch creation and updating of Elasticsearch index files from the command line

For Pega 8.6 you can follow: Rebuilding search indexes by using a direct connection to the database and Checking search index status

All resolved issues for the latest 8.6x patch can be found here: Pega Platform 8.6.6 Patch Resolved Issues

 I found one client who had a Cloud environment where the issue occurred  because of a faulty configuration  base where a cleanup of older nodes did not happen  and it picked random util nodes to attach and caused ES corruption. Web node accidently updates replica count which creates impacts Search Stability.  

That issue was resolved in 8.6.6 under BUG-747182

Replica count updated only for index nodes Every time a search node is restarted or reinitialized, a refresh command (refreshClients command) is sent to all nodes. A web node which is not a search node will start a reinitialization designed to reattach the node to ES cluster, and it was expected that the web node would not change information about the replica count since it is not responsible for storing data. However, the non-search node was changing the replica count due to a condition created when locking was not ready on the search node. This has been resolved with an update to insure replica count is updated only for index nodes in PegaSearchProviderImpl::reInitializeESNode.

Therefore it might be worthwhile to update to 8.6.6 to test your use case.