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But I still am not sure whether I can follow. Do you mean the links in the menu settings? Or somewhere in a redirect rule of my plugin? Or in the widget?
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>> It depends on where you put the links to the Registration form. I put mine on a menu item on a widget. So I had an item there that said “Sign up” and I just refreshed the link URL. But like I said, the link was originally “wp-login.php?action=register” so I deleted that. Saved. Waited a few seconds. And then put it back in. And then it worked fine. I’m sure the glitch happened when I updated. I guess the LINK just needed to be “refreshed.”