No audio in breakout room for mac user

We have just tested the Twine plugin for managing speed networking in breakout rooms which worked well. However, one test user on a mac had no sound when she was moved into a breakout room although it was fine in the main meeting. The other person in the breakout room with her  was also affected and they lost sound too until they were moved into different rooms. So , the mac user stopped the sound for both participants in the breakout room but all fine in the main room. Any ideas?