A feature of the gateway is that it can serve queries without a kafka connection. However, if the kafka client is connected the gateway might stall when attempting to publish reports. This can occur when the topic being published to does not exist and the gateway does not have capabilities to describe & create the topic.
The expected behavior is for the gateway is to log an error on failure to send the message and drop the message. Hopefully there is a configuration option for rdkafka to enable this behavior in the underlying librdkafka.