wp-admin page has a "redirect loop" for every site on webhost

I use Web Hosting Hub for hosting most of my sites and since yesterday, I cannot access the */wp-admin page to log into wordpress for all these sites.

Error on firefox: The page isn’t redirecting properly
Error on chrome: This webpage has a redirect loop

The sites themselves are all up but I cannot gain access to the wordpress backend. All are different sites with different themes, different versions of wordpress (some latest) and there are only a few plugins common to all:
Statcounter
Limit login attempts
Wordpress SEO (by Yoast)
Backup wordpress

I contacted my webhost about it and they gave an ambiguous answer “I have check into this and it does look like this is an issue with your .htaccess file. It looks like you have some custom code in your .htaccess file. You will either need to fix the code or recreate the .htaccess file. I would recommend reaching out to a developer that is more familiar with coding.”

I never manually modified my htaccess files. Here is one of the htaccess file contents:
=====================================

# 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

=====================================

So I guess the first question is, what is ‘customized’ about it and why would it break the wordpress admin login page?