🧐可关闭[问题]使用splitMenu: true和mix模式后，路由设置二级路由或三级路由，点击二级菜单或三级菜单后，左侧菜单栏消失

提问前先看看：

https://github.com/ryanhanwu/How-To-Ask-Questions-The-Smart-Way/blob/main/README-zh_CN.md

### 🧐 问题描述

{
path: '/',
name: '首页',
routes: [
{
path: '/routeDemo',
name: '管理页',
component: './routeDemo'
}
]
}

点击二级菜单后，左侧菜单栏直接消失了。

### 💻 示例代码

### 🚑 其他信息

Start by reproducing the supplied splitMenu: true and mix-mode configuration with the nested routeDemo route, then trace the navigation entry point handling second- and third-level menu clicks. Done means the left menu remains visible after selecting either nested menu level; the payload names no source file or test.

Written by the indexing model from the issue text.