As shared earlier, once the user completes the payment successfully in the registration flow with the membership and order gets placed then the membership gets assigned to him and he becomes the vendor and gets redirected to the vendor store set up wizard.
Now as per the default flow if the user does not complete the payment for the membership plan after filling up the registration form and does not places the order then he becomes a pending vendor and no plan gets assigned to him.
On your live site as the flow is still not working, kindly check the shortcode added in the WooCommerce my account page and there add the correct shortcode. As on your staging site the issue got resolved after correcting the WooCommerce my account page shortcode.
Let us know if you need any further assistance from our end.
