打开一个内容很大的脑图，前端提示“连接异常，请刷新重试”

后端case-server日志：
前端network信息：
前端console信息：

从后端日志来看，是挺正常的，用户建立连接后，将脑图的json发到前端，但后端日志显示发送脑图json完成后，前端的network是没有看到接受到该message的(可能是前端处理中或者接受中)，直到前端提示异常，network才看到脑图json的message，后端日志显示连接被关闭。前端console显示错误信息。

Reproduce the problem by opening a very large mind map, then inspect the case-server logs alongside the frontend Network and Console information mentioned in the issue. Done means the mind map JSON is received and displayed without the frontend reporting a connection error or the server connection closing.

Written by the indexing model from the issue text.