backend http to https random redirection

Here is the .htaccess:

# BEGIN W3TC Browser Cache
<IfModule mod_deflate.c>
    <IfModule mod_headers.c>
        Header append Vary User-Agent env=!dont-vary
    </IfModule>
        AddOutputFilterByType DEFLATE text/css text/x-component application/x-javascript application/javascript text/javascript text/x-js text/html text/richtext image/svg+xml text/plain text/xsd text/xsl text/xml image/x-icon application/json
    <IfModule mod_mime.c>
        # DEFLATE by extension
        AddOutputFilter DEFLATE js css htm html xml
    </IfModule>
</IfModule>
# END W3TC Browser Cache

AddHandler php5-script .php

php_value memory_limit 300M
php_value max_execution_time 0

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

</IfModule>

# END WordPress

I deleted cookies, temporary files, etc and tried it in different computers, browsers and operating systems and the final result is the same. It is still happening.
I guess is something related to the theme, css, js… Sometimes the website doesn’t load properly…

Do you know where I can check the errors of my template while loading?

I will turn on the debugging feature soon. Before doing that I want to say that I have 3 more blogs under the same network and they have the same issue.
While navigating through wp-admin, you get the message that says that the content isn’t secure and the SSL certificate doesn’t belong to current domain (because I’m getting redirected to https and i’m not using a certificate for my domain). Saying that, I guess there is a problem with the server of the hosting company. It’s a shared hosting. I’m planning to build a development environment to test it with a duplicate of the site.
I’ll tell you what happened…

That explains a lot of issues. I will get a VPS!!!