router.urlFor() issue reproduction

controllers.application.js

import Ember from 'ember';
import { inject } from '@ember/service';
import { computed } from '@ember/object';

export default Ember.Controller.extend({
  router: inject(),
  fooBarUrl: computed(function() {
    return this.router.urlFor('foo.bar', 123, 456);
  }),
  bazQuxUrl: computed(function() {
    return this.router.urlFor('baz.qux', 123, 456);
  })
});

router.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

const Router = EmberRouter.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('foo', {path: '/foo/:id'}, function() {
		this.route('bar', { path: '/bar/:id' });
  });
  this.route('baz', {path: '/baz/:bazId'}, function() {
		this.route('qux', { path: '/qux/:quxId' });
  });
});

export default Router;

templates.application.hbs

<ul>
  <li>{{fooBarUrl}}</li>
  <li>{{bazQuxUrl}}</li>
</ul>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}