Try to find a theme which doesn't conflicts. Most of WP themes should work fine, because wpForo has 9k active installation and your bug report is the first.

We'll continue checking this and I'll update this topic once I got some news related to incompatible themes.

ok 2016 works, but now could you tell me what is the difference, so I can make your forum work with my theme ?

Problem : the theme is MY theme lol. Made with themeler.

I asked themeler authors to take a look at this compatibility issue. I'll keep you informed.

I have an answer : le wfp-menu class is not here

They made me add it with jQuery in the theme :

jQuery(function ($) {
   $("#wpf-menu").addClass("wpf-menu");
});