When a network error occurs during operation execution, the pool for the selected server is cleared. When the Connection that generated the error is then dropped, it attempts to check itself back into the pool, but since the pool has been cleared in the meantime, it closes itself as stale. Instead, this error-originating Connection should close itself with ConnectionClosedReason::Error.

Because of this, it is currently impossible for a Connection to be closed with ConnectionClosedReason::Error.