react-router 同构生成的key值不一致

Question

//服务器端
koa2Router.use(async (ctx, next) => {
            const memoryHistory = createMemoryHistory(ctx.url);
            const history = syncHistoryWithStore(memoryHistory, store, {
                selectLocationState (state) {
                    return state.get('routing').toObject();
                }
            });

            await next();
        });

//前端
const history = syncHistoryWithStore(browserHistory, store, {
    selectLocationState (state) {
        return state.get('routing').toObject();
    }
});

log:

//服务器端
 { type: '@@router/LOCATION_CHANGE',
   payload:
    { pathname: '/vols/678',
      search: '',
      hash: '',
      state: null,
      action: 'POP',
      key: 'ofet3q',
      query: {},
      '$searchBase': { search: '', searchBase: '' } } }
      
      
//前端
action: {
    payload: {
        pathname:"/vols/678",
        search:"",
        hash:"",
        state:null,
        action:"POP",
        key:"pe6t4r",
        query: {},
        $searchBase: {
            search:"",
            searchBase:""
        }
    }
}

//除了key值不一致外,其他信息都一样,但为什么生成的key值会不一致呢?