'No', 'Maybe' & 'I'm attending' Not visible.

These buttons aren't visible, and I know I must be missing something. I have changed the active theme (from Pagelines to Twelve), I have deactivated all non-wpmu plugins, I have tried single and recurring events. I am using the membership plugin as well, so I have logged in separately with a different browser on a different account on each membership level. Anything obvious in settings for this I am missing? Thanks for your time.