Hi Sheldon,
Thank you for contacting Syncfusion support.
We are unable to reproduce the reported issue in the TreeMap component (v20.1.0.50) with the provided version. However, we can reproduce the issue in the previous version (19.4.0.56). So, you can resolve the reported issue by updating the latest scripts and packages in your application. Please find the video below for your reference.
Video: https://www.syncfusion.com/downloads/support/directtrac/general/ze/Treemap-2137116349
Please follow the below documentation link to refer the latest script files of the component in the Blazor application.
https://blazor.syncfusion.com/documentation/common/adding-script-references
Please let us know if you need any further assistance.
Regards,
Indumathi R.