I’ve never tried this so I might be completely off the rails here buuut… Even if the second time it redirects you to wp-admin, isn’t that kinda pointless if you want a custom login page? What if you actually create a dashboard page and add a ProForm with the action set to login?
Yes, that would be a solution, but then what’s the use-case for the custom login URL field in the Backend Designer, if not that?
I got redirected to wp-admin after log in, so I can see the backend. That’s fine. But if I access to /wp-admin being logged out, then that page doesn’t work. Which is OK because I have my custom login URL set!