Can't follow friends

[user-removed]

I open the app -> click menu button (3 bars) -> click my name down the bottom -> click on the add friends button (top right) -> click on the add friend button next to my friends names, and as I scroll down I select more friends, then when I scroll up, the checkbox icon (selected friend) disappears and it's back to the add friend icon again, as though I never selected the friend.

I have iOS 9.2 on my iPhone 6s+ 64GB