Is your WordPress a multi-site installation? In this case members are filtered by subSite, they are no longer together.
It's not a multi-site installation.
The whole thing is very weird, Users that joined 2 days ago where processed properly, while the ones that joined a week ago were still only in the WP users list.
I've noticed that the "Our newest member" didn't update as well, but after using the "Delete All Cache" in wpForo it was sorted.
I'll update in a few days.