Method need to be

    protected function getFrontendUser()
    {
        if (PluginManager::instance()->hasPlugin('RainLab.User')) {
            $rainLabAuth = \RainLab\User\Classes\AuthManager::instance();
            if ($rainLabAuth->check()) {
                return $rainLabAuth->getUser();
            } else {
                return null;
            }
        } else {
            return null;
        }
    }

Instead of (when plugin is activated returning null)

    protected function getFrontendUser()
    {
        if (PluginManager::instance()->hasPlugin('RainLab.User')) {
            return null;
        }

        $rainLabAuth = \RainLab\User\Classes\AuthManager::instance();
        if ($rainLabAuth->check()) {
            return $rainLabAuth->getUser();
        } else {
            return null;
        }
    }

Chrome Warning:

[DOM] Found 2 elements with non-unique id #bloghubCommentSection6368b0bd2e5b6_username: (More info: https://goo.gl/9p2vKq) 
<input id=​"bloghubCommentSection6368b0bd2e5b6_username" type=​"text" name=​"comment_name" value=​"Sam" placeholder=​"Your Username" class=​"form-control" readonly>​
<input id=​"bloghubCommentSection6368b0bd2e5b6_username" type=​"text" name=​"comment_user" autocomplete=​"off" value placeholder=​"Your Username" class=​"form-control from-control-bloghub-special-assignment">​

Theme based meta declarations aren't stored on new posts, only on existing ones. Probably happens on general-declared meta values as well.

• Found in OC 3.1 (may occurs on previous releases as well)

Not sure which version of MySQL you are using on your local dev env? But it does not migrate properly on

 mysql --version
mysql  Ver 8.0.23 for osx10.16 on x86_64

I think a solution would be to remove the default value

- v1.0.0 Initial Release of RatMD.BlogHub
Rollback failed! Reason: "SQLSTATE[42000]: Syntax error or access violation: 1101 BLOB, TEXT, GEOMETRY or JSON column 'posts' can't have a default value (SQL: create table `ratmd_bloghub_visitors` (`id` int unsigned not null auto_increment primary key, `user` varchar(64) not null, `posts` json not null default '[]', `created_at` timestamp null, `updated_at` timestamp null) default character set utf8mb4 collate 'utf8mb4_unicode_ci' engine = InnoDB)"

In Connection.php line 669:
                                                                                                                                     
  SQLSTATE[42000]: Syntax error or access violation: 1101 BLOB, TEXT, GEOMETRY or JSON column 'posts' can't have a default value (S  
  QL: create table `ratmd_bloghub_visitors` (`id` int unsigned not null auto_increment primary key, `user` varchar(64) not null, `p  
  osts` json not null default '[]', `created_at` timestamp null, `updated_at` timestamp null) default character set utf8mb4 collate  
   'utf8mb4_unicode_ci' engine = InnoDB)