Prevent /wp-admin/ from redirecting to homepage?

In my case, it ended up being some kind of adverse interaction in the nginx wordpress config that I had. Something about not passing along the naked arguments:

        location / {
original line:               try_files $uri @php;
new line:        try_files $uri $uri/ /index.php?$args;
        }

And the associated upstream was wrong. Used the config suggested here: https://www.nginx.com/resources/wiki/start/topics/recipes/wordpress/
For a simpler wordpress nginx config and that solved it.