My worst bug had me using statistics to try and correlate occurrence rates with traffic/time of day, API requests, app versions, Node.js versions, resource allocations, etc. And when that failed I was capturing Prod traffic for examination in Wireshark...
Turned out that Node.js didn't gracefully close TCP connections. It just silently dropped the connection and sent a RST packet if the other side tried to reuse it. Fun times.
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