Steps to reproduce the issue

1. Go to http://demo.joombri.in/component/users/?view=login
2. Type username freelancer and password password.
3. Click on Log in button.

Expected result

Expected to login successfully.

Actual result

Fatal error: Cannot redeclare class Composer\Autoload\ClassLoader in /home/joombrii/public_html/demo3/libraries/vendor/composer/ClassLoader.php on line 43

System information (as much as possible)

Joomla 3.9
PHP 7.0

Additional comments

This error is coming on another domain www.joombri.in as well.