Meeting participants not showing up on breakout room list

Occasionally when staff create breakout rooms, some participants do not show up on the breakout room list. We have resorted to asking those participants to leave the meeting and re-join, which sometimes works and results in us being able to assign them to a room. However, there are some individuals who still do not show up in the breakout room list even after exiting and re-joining the meeting. Is this a known issue?