Unified Alerts cannot detect existing Prometheus data source after v8.5.4-v8.5.11 upgrade

Created unified alerts in Grafana v8.5.4 that worked initially worked querying a Prometheus data source. Then upgraded to v8.5.11 and the alerts constantly fire because they cannot locate data source for query.

Attempts to select existing data source and save again give the message below.

Creating a new folder and then recreating alert assigned to new folder can locate data source. Do not know what caused the bug.