Dashboard URL links to https://wp-admin

The problem I’m currently having is that when I try to access the dashboard of a website (non-main) instead of going to https://sub.domain.com/wp-admin, it goes to https://wp-admin.

This problem occurs from both the admin-bar and the Network Admin Sites list. The website itself at sub.domain.com is accessible, but not the admin or login pages.

I copied the wp-config.php and web.config directly from the Network Setup as instructed but it just doesn’t work.