Custom unsubscribed confirmation page not working

My Mautic version is: v2.15.3
My PHP version is: 7.1

My problem is:
In the “Email settings” page there is a section called “Unsubscribed confirmation message”. Here I want to change the default message to something custom. I added some HTML code with a button that invites the unsubscribed users to take an action.

The problem is that after I save, the users are still redirected to the default message. No matter what I add here, even plain text without HTML code, the users see the original message…the one that starts with “we’re sorry to see you go…”

The thing is after I save, my changes appear inside the section, but they don’t work on a real campaign.

Does anyone know how can I fix this issue and make mautic display my custom message?

Thank you