Users (Mobile Workers) couldn't login after elastic search failure due to power interruption and storage space. I have reallocated shards of the indices after the disk storage is expanded and all indices are green now.
user's login issue is unrelated to elastic search (ES) issue. from the screenshot you shared, ES is healthy and you don't need to regenerate indices.
the other issue you raised is disk space, I remember a ticket related to this: Error while trying to add remote reports to the local - #6 by dan
cause of issue:
couchdb_proxy's disk space was full or no space left on disk . CouchDB is unable to perform its operation. the solution was clearing old logs of ES service, which is shared with the couchdb_proxy server.