Apache redirecting to HTTP for subdomains after adding trailing slash

Question

I edited the question based on new information.

I know I am a big novice for server configuration stuff.

What I noticed is that mod_dir adds backslash properly in all non-subdomain paths.

For example: https://example.co/test => https://example.co/test/

But when I have a subdomain: https://sub.example.co/test => http://sub.example:443/test/

Here is my default-ssl

 ExpiresActive On
 ExpiresDefault "access plus 1 month"
 Protocols h2 h2c http/1.1
 Alias "/library/" "/var/www/html/example/library/"
 <Directory /var/www/html/>
  Options FollowSymLinks MultiViews
  AllowOverride All
  Order allow,deny
  allow from all
 </Directory>
 <FilesMatch "\.(cgi|shtml|phtml|php)$">
  SSLOptions +StdEnvVars
 </FilesMatch>
 <Directory /usr/lib/cgi-bin>
  SSLOptions +StdEnvVars
 </Directory>
 <VirtualHost _default_:443>
  ServerName example.co
  DocumentRoot /var/www/html/example
  SSLEngine On
  SSLCertificateFile /etc/letsencrypt/live/example.co/cert.pem
  SSLCertificateKeyFile /etc/letsencrypt/live/example.co/privkey.pem
  SSLCertificateChainFile /etc/letsencrypt/live/example.co/chain.pem
 </VirtualHost>
 <VirtualHost *:443>
  ServerAlias sub.*
  DocumentRoot /var/www/html/example/sub
 </VirtualHost>

Here is my 000-default

<VirtualHost *:80>
 RewriteEngine On
 RewriteCond %{HTTPS} off
 RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI}
</VirtualHost>

Why do my subdomains throw errors and change into HTTP when mod_dir adds directory slashes?