I'm afraid that templates are not automatically discovered before Symfony 4.4
If you can't upgrade Symfony, you'll need to manually add bundle path to your paths.

I just tried on a project with Symfony 4.4 and KnpPaginatorBundle 5.0 and I can confirm that it's working

I am experiencing the same issue in Symfony 4.4 and KnpPaginatorBundle 5.0

The Symfony version has just been upgraded, which seems to have caused this issue.

The Symfony version has just been upgraded, which seems to have caused this issue.

What do you mean?

As already mentioned, I can't reproduce this problem on Symfony 4.4/KnpPaginatorBundle 5.0

I have a Symfony instance that . has just been upgraded to 4.4 and KnpPaginatorBundle and I have had to manually register the twig namespace to make it work. I have the same issue with Symfony v 5

Please provide output for console de:conf twig

I can reproduce the funcionality on Symfony 5, so I have to close this issue.
If you're able to reproduce it, feel free to re-open.
Here are steps for a minimal Symfony 5 project that is able to run this bundle:

composer create-project symfony/website-skeleton mybigproject
cd mybigproject
composer require knplabs/knp-paginator-bundle symfony/web-server-bundle:^4.4
vi config/packages/knp_paginator.yaml # add configuration as above
bin/console make:controller
vi src/Controller/VictoriousKangarooController.php #edit as below
vi templates/victorious_kangaroo/index.html.twig #edit as below

here is the controller

<?php
namespace App\Controller;
use Knp\Component\Pager\PaginatorInterface;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\Routing\Annotation\Route;
use Symfony\Component\HttpFoundation\Request;
class VictoriousKangarooController extends AbstractController
{
    /**
     * @Route("/victorious/kangaroo", name="victorious_kangaroo")
     */
    public function index(PaginatorInterface $paginator, Request $request)
    {
        $pagination = $paginator->paginate(range(1, 99), $request->query->getInt('page', 1));
        return $this->render('victorious_kangaroo/index.html.twig', [
            'controller_name' => 'VictoriousKangarooController',
            'pagination' => $pagination,
        ]);
    }
}

in template, just add {{ knp_pagination_render(pagination) }}

Thank you @garak

I did some tests and managed to run normally with a new instance of symfony (4.4 and 5.0). Apparently my problem comes from the conflict of another bundle.

I'm debugging to better understand what happens with this legacy application.

Just add

paths:
    '%kernel.project_dir%/vendor/knplabs/knp-paginator-bundle/templates': KnpPaginator

to twig.yaml

https://symfony.com/doc/4.1/templating/namespaced_paths.html#registering-your-own-namespaces