I have droplet running Ubuntu 16.04 and LAMP stack

I have 3 sites enabled:
one at /var/www/html (default apache config)
two at /var/www/others/SITE/public_html

My sites are showing well, but one of then sometimes shows my site and sometimes shows apache default page

Notice, there is no default page at /var/www/html/index.html because I my first site are installed there. All said, my ‘It Works’ page is the Digital Ocean version, instead the regular apache (that is sometimes shown on my site).

You can check this behaviour at:
drg.adv.br

When I open a private window the website sometimes shows the apache default page, I close the page, open private window again and my regular website.

My apache conf:

cat /etc/apache2/sites-enabled/drg.adv.br.conf 
<VirtualHost *:80>
    ServerName drg.adv.br
    ServerAlias www.drg.adv.br

        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/others/drg.adv.br/public_html

        <Directory /var/www/others/drg.adv.br/public_html/>
        Options Indexes FollowSymLinks
            AllowOverride All
            Require all granted
        </Directory>

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

        <IfModule mod_dir.c>
            DirectoryIndex index.php index.pl index.cgi index.html index.xhtml index.htm
        </IfModule>

</VirtualHost>

Ls to site folder:

ls /var/www/others/drg.adv.br/public_html/
css  font  images  index.htm  index.html

What I’m missing?

This should be due to high acess to the site?