Analytics Reporting API 409 Conflict on AU-1 BYOC

Need some troubleshooting help with a 409 Conflict when creating a custom report via the Analytics Reporting API on our AU-1 BYOC instance. The payload validates locally but fails on deployment. Using Python SDK v3.5.1. The report ID is auto-generated, so no manual collision. Any known restrictions on metric combinations for BYOC tenants?