Deflector exists as an index and is not an alias. Again

Graylog Central (peer support)
2

We are running Elasticsearch 1.7.3, Mongodb 3.4.15, and Graylog-Server 2.3.2 on Ubuntu Server 16.04. All is running on same server.

I’m pretty sure that one of the above Versions does not match - Elasticsearch or Graylog - as those both are not compatible. If they work you are in unsupported stage that was never tested!

You can find the answer in our FAQ

http://docs.graylog.org/en/2.4/pages/faq.html#how-do-i-fix-the-deflector-exists-as-an-index-and-is-not-an-alias-error-message