This happened today when me and Danny were going over the app. In one event (Hufflepuff huff n' puff).
Steps to reproduce: Try removing all participants one by one from top. At one point the "Save" button vanishes and you can't do anything more. There were no console errors.
Browser: Safari.
The fix works fine. I'm slightly concerned that the new placement of the Save Participants button is not that great. It looked great in the mocks but now that I'm adding fifty participants, I am realizing that people might miss that button completely. I'm not sure what the right fix for that is. We could wait until beta testing or until we have a chat with Sati to see what she thinks of it. In any case, that doesn't belong to this ticket.