Hi,
Thanks for your feedback on the FAQ. I've updated it.
I think no one reported on this in the past as the main documentation page for the configuration page had up to date information about this:
www.hikashop.com/support/documentation/5....html#checkout_login
So as mentioned there now, the problem is that you removed the "login" view from your checkout workflow. You need to add it back, and then select the "guest" mode in the "registration" setting.
Also, as a side note, I don't recommend you to change the "New User Registration Group" setting. You should keep it to "registered" or you want to turn off the "Allow User Registration" setting: Either you allow registration from the Joomla registration form with the normal user group, or you turn off the Joomla user registration, so that you'll only have guests on your website.
By selecting "guest" in that "New User Registration Group" setting with the registration allowed, users will be able to register on your website via the Joomla registration form page, but their account won't have a valid user group, which they won't be able to use to login on your frontend.