Some themes depending how they display the menus can cause a conflict with the menu displaying on mobile devices, the theme has different settings to try and fix this conflict, but some themes it still is an issue, so I was thinking the other day to myself,
self, what if I set up the forum as a subcategory on the menu,
so I did
add a link to the menu and put a hashtag in the url, it's also important to have a icon along with it, then drop the forums page right underneath and whatever else you want, I use theme my login, so I dropped my login/logout pages there as well as register and lost password
and it works perfectly
your mileage may vary