http on subdomain redirects to main domain; subdomain works with https

Question

I have a root domain https://example.com and subdomain https://sub.example.com, and a Positive SSL on the root domain example.com

My problem is that whenever I try to visit http://sub.example.com I am correctly redirected to https://example.com, but when I visit https://sub.example.com, I am not redirected. How can I also redirect https://sub.example.com to https://example.com ?

.htaccess in subdomain:

# BEGIN WordPress
<IfModule mod_expires.c>
    ExpiresActive On
    ExpiresByType image/jpg "access plus 6 hours"
    ExpiresByType image/jpeg "access plus 6 hours"
    ExpiresByType image/gif "access plus 6 hours"
    ExpiresByType image/png "access plus 6 hours"
    ExpiresByType text/css "access plus 6 hours"
    ExpiresByType application/pdf "access plus 1 week"
    ExpiresByType text/javascript "access plus 6 hours"
    ExpiresByType text/html "access plus 10 minutes"
    ExpiresByType image/x-icon "access plus 1 year"
    ExpiresDefault "access plus 3 hours"
</IfModule>
Header set X-Endurance-Cache-Level "2"

# END WordPress

<IfModule mod_rewrite.c>
    RewriteEngine on
    RewriteCond %{HTTP_HOST} ^sub\.example\.com$ [OR]
    RewriteCond %{HTTP_HOST} ^www\.sub\.example\.com$
    RewriteCond %{REQUEST_URI} !^/\.well-known/acme-challenge/[0-9a-zA-Z_-]+$
    RewriteCond %{REQUEST_URI} !^/\.well-known/cpanel-dcv/[0-9a-zA-Z_-]+$
    RewriteCond %{REQUEST_URI} !^/\.well-known/pki-validation/[A-F0-9]{32}\.txt(?:\ Comodo\ DCV)?$
    RewriteRule ^/?$ "https\:\/\/example\.com\/" [R=301,L]
</IfModule>

Any help or suggestions would be much appreciated.

Answer 1

Your conditions are only looking HTTP requests

RewriteCond %{HTTP_HOST} ^sub\.example\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.sub\.example\.com$
RewriteRule ^/?$ "https\:\/\/example\.com\/" [R=301,L]

Try to add same rules with HTTPS

RewriteCond %{HTTPS_HOST} ^sub\.example\.com$ [OR]
RewriteCond %{HTTPS_HOST} ^www\.sub\.example\.com$
RewriteRule ^/?$ "https\:\/\/example\.com\/" [R=301,L]