We are experiencing the same thing, but we manually create b/o rooms during the meeting. This has been going on for about two weeks now. After assigning participants to breakout rooms and then returning to main, those assignments are randomly forgotten. To-recreate:
1. manually assign participants to b/o room
2. send to b/o room
3. return to main
4. b/o assignments are randomly unassigned (some remain in b/o, some become unassigned)
5. manually RE-assign participants to b/o rooms
6. send to b/o room
7. return to main
8. b/o assignments are randomly unassigned AGAIN (and different people are unassigned)
9. repeat process over and over and over
We send to b/o rooms regularly during a meeting and this defect makes it super inefficient.