I have 2 posts in the same forum, one with navigation and one without. What am I missing?
Try to fix Autoptimize errors from wpforo assets (exclude them).
The posts are correct.
In the threaded layout, the topic posts pagination is based on the number of parent posts. Parent posts are not replies, they may have many replies and all those will be on the same page under that parent post.
Please follow this doc for more info: https://wpforo.com/docs/root/categories-and-forums/forum-layouts/threaded-layout/#thread-managing-options