Couldn't find any existing threads about this and can't figure out if it is a setting.
Basically, I have a few subforums. When I post in a subforum, it's not showing up on the last poster info on the main forum page. You can have a look - https://adminloop.com/forum/ . Just posted a topic in the Forum Games section subforum (near the bottom), but it's not showing up in the last poster information for General Discussion.
I'm sorry but wpForo only displays last post information from certain forum. In your case from "General Discussion" forum. SubForums last post information are being displayed on sub-forum when you enter in the "General Discussion" forum: https://adminloop.com/forum/general-discussion/