Had topics with no pagination for guest login. Sitemaps were not including these other pages.
Turns out the bug is due to a db call checking private=0 for topic posts and not counting those posts for items_count. The fix was to comment out the following section in class-posts.php
//If doesn't have "View Private Posts" access and not Owner, only return public posts
// $wheres = " " . $table_as_prefix . "`private` = 0";
This is not wpForo issue it comes from the MySQL version. Please see the description of the issue here: https://bugs.mysql.com/bug.php?id=81031
Here is the same issue:
Spoke too soon. The problem persists and the only working workaround is to comment out the offending code in class-posts.php. More details at: