koa's redirect function doesn't work well

Question

when I use ctx.redirect, koa just sends GET request but not actually redirect the tab to other page from where It was. I'm just trying to redirect to user's page after signup. Here's code.

signup

router.post('/signup', async (ctx, next) => {
    let data = ctx.request.body
    const param = await makeParam(data)

    try {
        const user = new User(param)
        await user.save()
        ctx.redirect(`/u/${data.username}`)
    } catch (e) {
        console.error("Failed to save post request", e, param)
    }
})

and here's the router for userpage

router.get('/:userName', async (ctx, next) => {
    let userName = ctx.params.userName

    let renderData = {
        userName: userName,
        profilePic: "",
        itemCount: "",
        contentCount: "",
        joinedDate: "",
        lastVisited: ""
    }

    await ctx.render('form/form4', renderData)
})