Analytics API 500 Error on Zendesk Metric Mapping

Struggling to understand why the Analytics API returns a 500 Internal Server Error when querying custom metrics mapped from Zendesk ticket fields. The endpoint /v2/analytics/interactions/query fails specifically when including the zendesk_priority dimension. Standard GC metrics work fine. This happens on EU1 environment. Is there a known limitation with custom attribute aggregation in the current reporting engine?