Looks like there is a missing rule in your htaccess file, try
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
# ensure access to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
RewriteCond %{HTTPS} off
RewriteCond %{REQUEST_URI} !^/wp-json/
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^ - [L]
#ensure you can access the network dashboard too.
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) wp/$2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ wp/$2 [L]
RewriteRule . /index.php [L]
You can test your htaccess rules with this tool.