OAuth2 Redirect Failure in Power BI Service

We're encountering a new issue with Power BI reports connected to SharePoint Online. Reports developed and refreshed successfully over the past year are still working, but newly published reports (as of today) are failing to refresh in the Power BI Service due to OAuth2 credential issues. Desktop fine, just the service. 

• All standard and advanced checks have been completed.
• Ownership of the report was transferred and credentials updated, but the issue persists.
• Attempting to edit credentials in Power BI Service results in a blank OAuth2 redirect page.
• Tested across:
  • Chrome
  • InPrivate mode
  • Multiple devices
• Redirects are allowed; no tracking or browser issues found.
• No recent known issues found after extensive research.
• A new test report using a different source and owner also fails in the same way.
• Existing reports continue to refresh successfully.
• Newly published reports fail due to inability to set credentials.
  
  

  Error Message

  The credentials provided for the Web source are invalid. The exception was raised by the IDbCommand interface.

  Redirect URL shown:

  https://preview.powerbi.com/views/oauthredirect.html?.....

  Cluster URI:

  WABI-UK-SOUTH-C-PRIMARY-redirect.analysis.windows.net

  
  
  
• Has anyone else experienced this issue recently?
• Are there any known changes to OAuth2 flows or Personal Cloud Connect in Power BI Service?
• Is this potentially a Microsoft platform issue affecting newly published reports only?