Authentication of [elastic] was terminated by realm[reserved] - failed to authenticate user [elastic]

I have an Elasticsearch cluster with version 7.3.2. The cluster was stopped because of the error " Authentication of [elastic] was terminated by realm[reserved] - failed to authenticate user [elastic]. Failed to retrieve password hash for the reserved user [elastic].".

Why it is happening and is there any solution to solve the issue?

This indicates that something is wrong with the .security index. The rest of the elasticsearch logs around this line would probably contain much more information if you can check or share with us here