I replaced the form with the one-button RSVP and the problem is gone, so it must be something with the form.
I uploaded a screenshot here: http://rawk.ca/pic.png
I wonder if the issue is with private groups. I couldn’t figure out why it was only showing seemingly random activities using [activity-stream primary_id=2 max=5] (2 is my private group id).
It basically selects everything in the bp_activity table with item_id = whatever you configure it for, but if ‘hide_sitewide’ is 1 (meaning it’s a private group), no activities will show.
Is there a way to show all activities of a private group?