The authors of the service experienced an incident where their proxy servers were stuck in a busy-loop, causing them to receive and bounce multiple pings. The issue was eventually traced to a bug in the Rust `tracing` library's `Subscriber` module, which is used for fine-grained span records. The problem arose because the `poll` function of a `Future` returns immediately when it reaches a `Ready` state, but the underlying async executor doesn't actually progress its state machine. This caused an infinite loop in the proxy servers. The issue was found to be related to the `TlsStream` type from Rust's `tls` library, which is used for TLS connections. A bug in this type caused it to spin out and trigger a busy-loop when a certain condition was met. The authors were able to identify the issue by analyzing the stacktrace and using instrumentation to monitor their proxy servers. They were able to fix the issue by updating the `tls` library and implementing additional testing infrastructure to detect such bugs in the future.