You have a bug in the template_render_output hook.
While the mod is active, the template_render_output hook code causes activity.php to fail to render forum ID's, Forum Names, and text previews from the .\vb\activitystream\view\perm\forum\post.php file. The new thread data still functions.
In which, it is apparently interfering with this line:
Code:
$foruminfo =& vB::$vbulletin->forumcache[$threadinfo['forumid']];
on post.php at line 88.
I've not a clue how those two correlated, but when i disable that hook from the addon of Require Edit Reason, activity.php renders new post text and forum ID/name without issue.