I have a wordpress site on main.com and a second one on blog.main.com

main.com already had an ssl certificate working.

In cPanel I installed a new wildcard ssl certificate intended for ‘*.main.com’

(sorry, apparently i don’t have enough reputation to post more than 2 links)

At this point:
https main.com was continuing to function properly.

http blog.main.com was still working.

https blog.main.com was redirecting to https main.com

So the blog needs more work.

I changed the wordpress site-url and site-address of the blog to ‘https://blog.main.com‘.

And I changed the .htaccess of the blog and added 3 lines on top:

RewriteEngine on
RewriteCond %{HTTPS} !=on [NC]
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Now:
https blog.main.com still redirects to https main.com.

http blog.main.com also redirects to https main.com.

(Changing the site-url and address and the .htaccess back, doesn’t reverse the redirect.)

The only redirect in cPanel is 403 for ‘.(htaccess|htpasswd|errordocs|logs)$’

edit: Note that mail.main.com is also redirecting the main.com.

What could be causing the blog to redirect to the main site.