I was looking to see how to actually report this, and am not quite sure how since the rabbitmq input plugin has no maintainer listed here: Logstash Plugins Community Maintainers
The rabbitmq input plugin isn't a community plugin so it has no community maintainer. It's a core plugin that's maintained by the Logstash team.
Regardless of how a plugin is maintained, discuss.elastic.co is the right place for questions. If you're reasonably sure you've found a bug, or if you have a feature request, file a issue in the GitHub project.