We upgraded today during our monthly patch cycle from 3.0.2 to 3.1.1. We also upgraded our Elasticsearch cluster from 6.8.2 to 6.8.3. All upgrades were done serially and Elasticsearch as a rolling upgrade. Afterwards, all connections and traffic flow appears normal to the three Graylog and three Elasticsearch nodes. The problem is that we cannot see any logs after the last Graylog node was upgraded. They appear (from connection and traffic volume) to be loading but do not appear in any query. Logs on both Graylog and Elasticsearch show nothing that would explain this.