Membership Cannot Find Reason Why Content Is Not Locked

I am using the latest version of the plugin

I have a site where I want people to register for free before they can use a form to submit info

For example this page is locked with a short code <register>

The short code did not lock the page and I then tried to lock the full page.

No luck.

I am doing something wrong but have no clue how to even describe it.
I therefore made short video - unfortunately the sound was muted but I am sure you'll get the idea.

The video is 8m and 5 mins long.