Looks like the newest version of User & Comment Mentioning is broken. Using WP 4.8.3 and PHP 7.0 we got a lot of errors:
For example:
[27-Nov-2017 14:25:47 America/Sao_Paulo] PHP Warning: trim() expects parameter 1 to be string, object given in /wp-content/plugins/wpdiscuz-user-comment-mentioning/WpdiscuzUCM.php on line 123
[27-Nov-2017 14:25:47 America/Sao_Paulo] PHP Catchable fatal error: Object of class WP_Comment could not be converted to string in /wp-content/plugins/wpdiscuz-user-comment-mentioning/WpdiscuzUCM.php on line 123
Could you provide any help?