Missing Error Message

At this location: https://www.comefriusa.com/wp-login.php?action=register
when a user registers with the same email address, they get a red empty box, instead of the “existing user” message. This was working fine until recently. Did something change? I’m afraid to update WordPress, since I’ve made so many manual changes to the code. Any idea how to fix?

Thanks so much!

https://www.ads-software.com/plugins/new-user-approve/