Flutter Web调试控制台无法访问已显示的本地变量问题求助

各位大佬好，我遇到一个Flutter Web调试的奇怪问题，想请大家帮忙看看：

我在VSCode里给代码打了一个断点，程序停在断点处后，在Variables -> Locals面板里明明能看到loadedMessages这个变量已经加载出来了，但我在Debug Console里输入这个变量名时，却收到了如下错误：

loadedMessages CompilationError: The getter 'loadedMessages' isn't defined for the class '$SimpleChatState'.
'$SimpleChatState' is from 'package:alpacalaw/blocs/simple_chat/bloc/simple_chat_bloc.dart' ('lib/blocs/simple_chat/bloc/simple_chat_bloc.dart').
Try correcting the name to the name of an existing getter, or defining a getter or field named 'loadedMessages'.

我的launch.json配置如下：

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Flutter Web",
      "type": "dart",
      "request": "launch",
      "program": "lib/main.dart",
      "args": [
        "-d",
        "chrome",
        "--web-port=5000",
        "--web-enable-expression-evaluation"
      ]
    }
  ]
}

我本来预期在Debug Console输入变量名后，能看到loadedMessages.toString()的结果，结果却出现了上述错误，有没有人能解释下这是怎么回事呀？

内容来源于stack exchange