Multiple participants' breakout room icon disappeared during a session

Hi! During a training session with participants in Mongolia, several of our participants no longer had the breakout room icon. They were also unable to find it by clicking "more." This was true of users on phones as well as laptops. One of them even left the meeting, completed an update, and joined the meeting again. Still, no icon. We use the self-select breakout rooms, and the majority of our participants did not have this issue.