It does show the last poster:

So, why not just specify it to allow me understand the issue?

wpForo has an adaptive design which hides some data on mobile to keep it clean and readable. You can use this CSS code to show last post information on mobile too. Put this CSS code in Dashboard > Forums > Settings > Styles > Custom CSS Code textarea. Save it, delete all caches, navigate to forum front-end and press Ctrl+F5 to reset browser cache:

@media screen and (max-width:620px) { 
#wpforo #wpforo-wrap .wpfl-2 .wpforo-last-post{display:block;} #wpforo #wpforo-wrap .wpfl-2 .cat-lastpostinfo{display:block;} #wpforo #wpforo-wrap .wpfl-2 .cat-title{width:40%;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-forum-info{width:60%;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-subforum li{width:60%; display:block;} #wpforo #wpforo-wrap .wpfl-2 .head-stat-lastpost{display:block;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-topic-stat-lastpost{display:block;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-topic-info{width:60%;} #wpforo #wpforo-wrap .wpfl-2 .head-stat-posts{width:10%;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-topic-stat-posts{width:10%;}
}
@media screen and (max-width:480px) {
#wpforo #wpforo-wrap .wpfl-2 .wpforo-last-post{display:block;} #wpforo #wpforo-wrap .wpfl-2 .cat-lastpostinfo{display:block;} #wpforo #wpforo-wrap .wpfl-2 .cat-title{width:40%;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-forum-info{width:60%;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-subforum li{width:60%; display:block;} #wpforo #wpforo-wrap .wpfl-2 .head-stat-lastpost{display:block;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-topic-stat-lastpost{display:block;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-topic-info{width:60%;} #wpforo #wpforo-wrap .wpfl-2 .head-stat-posts{width:10%;} #wpforo #wpforo-wrap .wpfl-2 .wpforo-topic-stat-posts{width:10%;}
}

ok ill try that