"Alert Rule returned no data" -- only when dashboard is not open in browser

Originally seen on v6.6.2 on Windows. Upgraded to v7.3.4 on Windows and the issue persists.

Backend is Elasticsearch 7.5.2.

When the dashboard is open in any browser, alerting works fine. The “test query” and “state history” all produce the expected results.

When the dashboard is not open in any browser, we get “Alert Rule returned no data” at the polling interval.