WebpackChunkName-Placeholder not working in mix?

I have this dynamically import (mix 6.0.6):

import(/* webpackChunkName: "request_user_profile_settings_[index]" */ '../modals/userprofilesettings.js')

which gives me a file named:

js/request_user_profile_settings_[index].js

I expected the placeholder [index] to be replaced with some number. What's going on?