Hello, @bijansaeedi
Hope you are doing well.
I can understand that the newly registered users are having some issues with login. I have tested the Login and Register feature and it is working perfectly in my development environment. I haven’t found any issue there.
But while inspecting your site, I have noticed something wrong there. On the Login section, The Username/Email field of the WP-Fundraising plugin has been replaced by another field that is related to a plugin named Digits. For that reason, the Username/Email isn’t getting recognized. The Markups are getting manipulated by the Digits plugin. You can check this screenshot for a better understanding.
Since that specific field of the WP-Fundraising plugin is getting replaced by the Digits plugin, you can check by disabling the Digits plugin or any functionality within the Digits plugin that can manipulate the login fields. In this way, you will be able to solve the issue. I hope you can understand.
Let me know if you need further assistance in this matter. I will be happy to assist you.
Best Regards,
Prosenjit