Your Plugin produces a lot of those notices:
Notice: Use of undefined constant info - assumed 'info' in ***/wp/wp-content/plugins/user-meta/classes/info.php on line 11
After this notice printed out, no headers can be set anymore. So then the your frontend is never shown.
Warning: Cannot modify header information - headers already sent by (output started at ***/wp/wp-content/plugins/user-meta/classes/info.php:11) in ***/wp/wp-includes/pluggable.php on line 934
I fixed it by modifying your info.php from
add_menu_page( 'User Meta', 'User Meta', 'manage_options', 'usermeta', array(__CLASS__, info));
add_menu_page( 'User Meta', 'User Meta', 'manage_options', 'usermeta', array(__CLASS__, 'info'));
But there are much more Notices shown. I think you should turn them on and fix those bugs. I can't turn off notices due to regulations of my university server.