Sankey Chart

Hi ArchStanton ,
Thanks for reaching out to Fabric Community Forum

The behavior you’re seeing is related to how Power BI handles custom visuals. According to Microsoft documentation, the functionality and supportability of a custom visual depend on the visual implementation, its certification status, and the support provided by the visual publisher.

Microsoft also mentions that AppSource custom visuals can offer both free and paid features, with feature availability controlled by the visual publisher. In addition, the behavior of organizational and other third-party visuals can vary based on the capabilities supported by that visual.

As a supported option, you may consider using a Microsoft-certified custom visual from AppSource, or alternatively use native Power BI visuals if you need broader compatibility across Power BI features.

Official Microsoft Documentation - 

Power BI custom visuals overview
https://learn.microsoft.com/en-us/power-bi/developer/visuals/power-bi-custom-visuals

Frequently asked questions about Custom visual license management
https://learn.microsoft.com/en-us/power-bi/developer/visuals/licensing-faq

Organizational visuals and third-party visual considerations
https://learn.microsoft.com/en-us/power-bi/admin/organizational-visuals

ArchStanton 
I kindly suggest working around with the sanky chart custom visual that you can install from Microsoft AppSource:
https://marketplace.microsoft.com/en-us/product/power-bi-visuals/wa104380777

Please take a look at the SQLBI video where they prepare the data to get a functional sankey chart:
https://www.sqlbi.com/articles/preparing-a-data-model-for-sankey-charts-in-power-bi/