A very common issue that happens is when adding the Wishlist Registration Widget registration form to the sidebar widget or shortcode inside the post/ page, but the registration form is not displayed.
In almost 100% of the cases it is because you haven’t checked the field inside the plugin’s settings: “Display widget to logged users”.
In this case you have 3 options:
1. Go to Wishlist Registration Widget’s settings and check the field to display the form to logged-in users
2. Log out and enter the page again
3. Open a new browser to see if the registration form appears