I noticed something interesting, there is no problem when I log out using the BuddyPress widget.
Do you have a multisite installation?
No.
Is WordPress installed in a sub-folder?
No.
What is the url you get when you try to logout?
With the WordPress toolbar: http://original-beast.revhost.fr/wp-login.php?action=logout&_wpnonce=323d408059&redirect_to=http%3A%2F%2Foriginal-beast.revhost.fr%2F%3Floggedout%3Dtrue
With the BuddyPress widget: http://original-beast.revhost.fr/wp-login.php?action=logout&redirect_to=http%3A%2F%2Foriginal-beast.revhost.fr%2F&_wpnonce=323d408059
What areas did you try to logout from? The WordPress Toolbar, bbPress login widget, something else?
WordPress toolbar.
Did this issue occur when you immediately activated bbPress? Or did the issue occur after a certain upgrade?
Only when bbPress is activated.
Did you have any cache plugins activated? Have you tried flushing the cache? If it is deactivated reactivate the plugin and flush the cache.
I don’t have any cache plugin.
Anything that can cache activated on your site, server cache, cloudflare, object cache, opcode caching?
I don’t have that.
What hosting provider do you have?
Revolta Hosting