Node Express Redis session not persisting after res.redirect()

I'm developing an application using the Spotify Web API. Every time a user logs in, the correct user data is being processed and stored to a Redis session. However on the FIRST login attempt, when I redirect to another route, a new, the app attempts to access a blank, new session. On subsequent attempts, the app accesses the correct session, and the app behaves normally. The cycle repeats every time I log out.

Relevant code:

Redis Store config in app.js

let RedisStore = require('connect-redis')(session);

let client = redis.createClient({
  host: 'localhost',
  port: 6379,
  //password: REDIS_KEY,
  db: 1
})
client.unref();
client.on('error', console.log)

app.use(session({
  store: new RedisStore({ client }),
  secret: REDIS_KEY,
  resave: false,
  saveUninitialized: false,
  rolling: true,
  unset: 'destroy',
  cookie: { maxAge: 3600000, sameSite: true, secure: false, httpOnly: false } // 1 hr
}))

Spotify API Callback route (the session is being fully saved here)

let set_json = new Promise((resolve, reject) =>{
    FUNCTIONS.set_json(req, new CLASSES.user_info(user_id, display_name, profile_picture, playlists));
    if (req.session.json) resolve(); else reject("error setting JSON");
})

set_json.then(
    function(set_success) {
        console.log("ID: " + req.sessionID);
        req.session.save(function(){
            res.redirect('/home');
        });
    },
    function(set_error){
        console.log(set_error);
    }
);

set_json function

exports.set_json = function(req, data) {
    let set_promise = new Promise((resolve, reject) =>{
        req.session.json = JSON.parse(JSON.stringify(data));
        if (req.session.json) resolve("success!"); else reject("error!");
    });

    set_promise.then(
        function(success){
            console.log(success);
        },
        function(failure) {
            console.log(failure);
            console.log("something went wrong!");
        }
    );
}

Home router, where the req.session I'd just set has seemingly been lost on the first login attempt. Subsequent login attempts successfully load the correct data.

exports.get_home = function(req, res, next) {
    console.log("ID: " + req.sessionID);

    res.render('home', { title: 'Spotify Playlist Optimizer', user: req.session.json});
}

Some example output:

First login attempt:

//Callback session id, holds correct data
ID: bvLDb6OwlBAPASAQqHBni2uIFfe-ASU3

//router session id, a blank, new session
ID: m2gEaduOyjde07b7aWvRVya4WkPze5M8

Subsequent login attempts until logout:

// Callback session id
ID: bvLDb6OwlBAPASAQqHBni2uIFfe-ASU3

// Router session id
ID: bvLDb6OwlBAPASAQqHBni2uIFfe-ASU3

// (matching and holding all needed data)