Recently, we encountered a production incident where PostgreSQL 16.8 became unstable, preventing the application from establishing database connections. The same behavior was independently reproduced in a separate test environment, ruling out infrastructure and configuration issues. Further investigation identified the pg_prewarm extension as the source of the problem. This blog post breaks down the failure, the underlying constraint, why it manifests only under specific configurations, and the corresponding short-term mitigation and long-term fix.