Please update the plugin to the latest v2.2.1. Now in “WooCommerce > Settings > Product Notes > Public Notes > Frontend Options” you will find a new checkbox – “Logged users only”. Please give it a try and let me know if something is not working as expected.
And if you like the plugin, please consider leaving me a rating here or here.
Hmm… That’s odd… Maybe you are using some caching plugin and simply didn’t clear the cache? If that’s not the case – maybe it would be possible for me to log in to your site and check what’s going on (my email is [email protected])? Please let me know if sharing an account is not an option, and I will continue solving it remotely.