I followed eshizero suggestion but modified another file and works fine!
This is the file: ganalytics.php in /modules/ganalytics folder
I simply add this line: .((!$back_office) ? 'ga(\'send\', \'pageview\');': '') at line 267
This is the new script
<script type="text/javascript">
(window.gaDevIds=window.gaDevIds||[]).push(\'d6YPbH\');
(function(i,s,o,g,r,a,m){i[\'GoogleAnalyticsObject\']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,\'script\',\'//www.google-analytics.com/analytics.js\',\'ga\');
ga(\'create\', \''.Tools::safeOutput(Configuration::get('GA_ACCOUNT_ID')).'\', \'auto\');
ga(\'require\', \'ec\');'
// 20180827 bugfix for analytcs pageview problem
.((!$back_office) ? 'ga(\'send\', \'pageview\');': '')
.(($user_id && !$back_office) ? 'ga(\'set\', \'&uid\', \''.$user_id.'\');': '')
.($back_office ? 'ga(\'set\', \'nonInteraction\', true);' : '')
.'</script>';