Hello,
I have installed the FOF Pages 1.0.4 on Flarum 1.3.1 and when I create a page, I do not see it in the back end panel but if I try to recreate one with the same name I get a warning that the slug is already taken.
Please check this video:
https://www.screencast.com/t/SACnF6QVGP
I also deleted the cache;