我有一个 Siesta 资源，我使用AddObserver. 现在，该资源使用的端点总是返回 404。大多数时候，观察闭包只会被调用一次并出现错误。但是，我有一个日志文件，其中我看到完全相同的错误（相同的时间戳和所有内容）被调用了两次。错误如下所示：
RequestError(userMessage: "Not found", httpStatusCode: Optional(404), entity: Optional(Siesta.Entity<Any>(content: "<h2>404 - Page Not Found</h2><p>The page could not be found.</p>", charset: Optional("utf-8"), headersNormalized: ["access-control-allow-headers": "Content-Type, Authorization", "set-cookie": "connect.sid=s%3APGOwgU4q3fhlxhag0E9Sc1zN_R9jTjH0.IAp%2BfAIfqxqP%2Bt5zZ1f0t1terpWgoRHpQhF%2BfB0gxyw; Path=/; HttpOnly", "etag": "W/\"40-ca3ea152\"", "via": "1.1 vegur", "content-length": "64", "content-type": "text/html; charset=utf-8", "date": "Sun, 17 Sep 2017 01:05:43 GMT", "access-control-allow-methods": "DELETE,GET,PATCH,POST,PUT", "connection": "keep-alive", "x-powered-by": "Express", "vary": "Accept-Encoding", "server": "Cowboy", "access-control-allow-origin": "*"], timestamp: 527303143.37699503)), cause: nil, timestamp: 527303143.37563998)
是否存在我应该两次收到此错误的情况？是否不能保证在这种情况下只调用一次观察者？是bug吗？？？是 Siesta、网络库还是我的代码中的错误？