Plugin never terminates

I figure someone here might know the answer and I'm just forgetting to implement something.

I've implemented my plugin in Rust using tonic and have the correct HealthService setup and correctly can serve the plugin and execute an RPC. However, when go-plugin goes to shutdown the plugin, I receive "plugin: plugin failed to exit gracefully" and the plugin is never killed (I have to manually SIGKILL/SIGTERM it). Is there something I need to be doing over on my plugin's implementation side (or the go-plugin side) in order to get this successfully killed?