Hello Vaidhyanathan,
Thanks for contacting the Pivotal Support Community!.
That said, the issue is that every member (including the restarted locator) needs to authenticate against the existing locator when joining the distributed system, you basically need to have the credentials configured for every single member. Please have a look at Security [1] for further details, and open a Support Ticket through the Pivotal Support Portal [2] (remember to include configuration files and logs) if you keep hitting this issue, one of our support engineers will be able to provide further assistance after reviewing the artefacts.
Best regards.
[1]: https://gemfire.docs.pivotal.io/98/geode/managing/security/chapter_overview.html
[2]: https://pivotal.io/support