The login problem was related to my domain configuration and the interaction with Joomla.
I updated the .htaccess file like:
RewriteCond %{HTTP_HOST} ^domain\.com [NC]
RewriteRule ^(.*)$ http://www.domain.com/$1 [R=301,L]
In this way, my users always get redirected to: www.domain.com Even coming to domain.com
This give them direct access, but is also beter for other plugin's and modules that use web-cloud services, depending on the www.domain.com (they will not work on domain.com) Examples: Social Login with Google/Facebook/Twitter; Map API's and other API's
I hope this will help some users! It helped me :-)