Reassigning a participant midway to a separate room / breakoutroom

If a participant leaves a separate meeting room in the meantime and returns to the plenary room, I can no longer reassign the participant to the separate meeting room. I only see that the participant is 'not participating'. I cannot select this participant in the 'Add participants' text box because the participant does not appear there. The participant remains standing under the separate meeting room with the text 'not participating'.

Previously, I could reassign a particpant without problems. What has changed in Zoom and how do I do this now? Or is this a bug?

Only if the participant completely leaves the meeting and then logs in again, can I select the participant again under 'Add participants' and add them back to the breakout room.