Redirecting to previous page after auto login

On the settings page, leave the redirect URL section blank/empty so it will use it’s default behavior.

Each landing page will need to have it’s own REGISTER button with a custom link like this:

So if the landing page is LandingPage1.html then the register link on that page would be:
https://mydomain.com/wp-login.php?action=register&redirect_to=http%3A%2F%2Fmydomain.com%2FLandingPage1.html

This will take you the registration page and then return you to the page you came from.

Hope this helps.