through the subscription form, users become registered users in the admin area
Either through the "subscribe" form, or otherwise, people become registered wordpress users. They immediately see the admin panel. And these are not bots. They are live users and write real comments. How so? It has become lately. After a series of updates. I do not want to put Google captcha, as the site loading speed is sharply reduced.
Don't follow you well. I'd suggest you read this FAQ: https://wpdiscuz.com/community/f-a-q/change-login-url/
Here is explained how to change the login URL.
If the link above doesn't help please leave some example URL to allow us to understand the issue.