I can read the forums OK using the Safari browser on ios but when I touch reply, the app opens.
When I touch logon up on the top right of the page, the app opens. The app is already logged on but does not affect the browser of course.
After some experimentation I found that I can access the forum using the link in the “what you can’t do in the IOS app” page and can successfully logon to it from there. Which is ironic, because the “what you can’t do in the IOS app” page actually says that you can’t access the forums from the app, but rather should use the browser.