Newly created user can't access admin side of subsite.

I have a brand new user that gets the error page every time they try to access the admin. I have made them an editor of the site in question. When viewing the site they have the admin bar showing that they have been logged in, but can’t access the backend. I have other users that can login and use the admin side fine on the same site.

The site is https://congress.archatl.com. I am forcing a subsite to be the main site in wp-config and wonder if that is causing my problem. I would love to figure out a better way to do that.

I feel like the config and htaccess are pretty simple and generic.

wp-config

define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', 'congress.archatl.com');
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 5);

.htaccess

# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]
# END WordPress

Can anyone give me a place to start looking deeper into this so I can fix it? Multisite is still pretty new to me.

Thank you.

jonathon