Ok, I’m fairly confused at this point. First, you said your were using hide page title to hide the title. Exactly where are you using that. I’m pretty sure that is not a global option. There is a per page option to hide the page title, so you have to do that for every page.
BUT – bbPress “pages” aren’t really pages, but instead are custom post types. For those pages that have a “page” to edit, you first have to enable the per page settings for custom post types, then edit on a per custom post type the per page hide title.
If you could describe an example of this forum of exactly what you might like to hide, I might be able to make more sense of what you want to do. But it is difficult to do that for forum topics since each one creates a new “page”.
And finally, it doesn’t make sense to me to want to do that. Consider the page that has this reply on it. It doesn’t make sense to me to want to hide the title of this topic. How would I know what I’m replying to without the topic title (which is a “page”).
If you want to hide the page title on EVERY page, add a Custom CSS rule: