There was an issue with the December release of Power BI that is causing this behavior in the visual. You can install the previous release of Power BI, and it should continue to work as expected.
That said we do have workflows as well to join the data to the polygons in Excel, publish to ArcGIS Online, then leverage Power Automate to pull back into Power BI. I'm not sure if this will help, but we can walk you through it if you need as a temporary workaround.