If you use custom login form, (e.g. ListingPro theme), and you:
- Can't login/sign up;
- "I'm a human" checkbox doesn't work; etc.
... then problem will most likely be that because you're using a custom login form, the necessary calls that WordPress login forms normally make are not being processed.
Unfortunately custom login forms need dedicated, custom code to work with systems like Shield that hook into them.
Also, if the form uses Social login... this is also not support by Shield as any necessary login protection provided by social logins are not compatible with WordPress logins.
If you intend to use custom login forms for your users, then you will most likely not be able to use Shield's login protection system.
WooCommerce provides custom login forms, and we support this, but this is because they provide the mechanisms to do this... unfortunately this isn't very common with custom-built forms.
We know this isn't the answer you'll be looking for, but is unfortunately the reality of using many different and independently developed products for WordPress.