Hi charles_o,
Since the same Salesforce report works as a new source, I would focus on the existing query. Verify that Include in report refresh is enabled, review the Applied Steps and refresh error, and reauthenticate the source in Power BI Service.
If the native query continues to fail, Power BI Connector for Salesforce provides an alternative token-based connection through an OData source.
AppExchange and 30-day free trial:
https://appexchange.salesforce.com/appxListingDetail?listingId=31526f0e-abd8-4cb5-bd1a-3bd56b5c0577
Docs and support:
https://metricasoftware.com/docs/salesforce/
https://metricasoftware.com/docs/salesforce/contact-support/
Cheers,
Metrica Team