Create breakouts based on poll's results: Grayed out!

Hi.

During our meeting today, I wanted to Create breakouts based on a poll's results. I ticked the box "Create breakouts" as I set up the poll.

Once I ended the poll, the option "Create breakouts" was grayed out, although it's activated on my personal and organisation/account-wide level. Any idea why?

I really need this option to work for a workshop next week.

Thanks!