The trace doesn't continue in kafka consumer side.
The kafka client is pulling message from server, the plugin also just traces the pull action. As that, you need to do the manual instrument before the pull action, and include the further data process.
Use Application Toolkit libraries to do manual instrumentation. such as @KafkaPollAndInvoke annotation at apm-toolkit-kafka or OpenTracing API, Or if you're using spring-kafka 2.2.x or above, you can track the Consumer side without any code change.