meeting attendees can't see each other

The past 2 meetings I have attendees have not been able to see each other when they are in main room. I (host) can see them and they can see me but no other attendees can see each other? I have had to make each one of the attendees a co-host for them to be able to see each other. I have not changed any settings and need to fix before next meeting. Please advise asap.

Thank you in advance! 

Carl