Hey @Mark07, thanks for the report. We had a bug on that visualization, which we fixed today and updated your site with the fix. Let me know if anything else is amiss.
The sentiment module in Discourse AI requires some models for sentiment and emotion classification. This comes pre-configured for customers in our hosting and works out of the box.
People self-hosting Discourse who want to use this feature will need to run those AI models and configure it in that screen for it to work.
That is documented at Self-Hosting Sentiment and Emotion for DiscourseAI.