I know that this is not the first post about this question, but I do it because others answers didn't solve my problem.
I tried the basic :
$kernel = new AppKernel('prod', true);
But this is not the good way to do it because I still have Symfony errors... I don't know how to rewrite errors pages :
http://le-blog-etudiant.fr/blablabla
Do you know if this Symfony error is caused by the fact that my website is still in dev mode or because my error.html.twig
page doesn't work ?
EDIT 1 :
I'm using app.php
on my site, I set $kernel = new AppKernel('prod', false);
and I did the command : php bin/console cache:clear --env=prod
but it still display Symfony's errors