Workaround
Downgrade the group series software to 4.0.x version.
Permanent
AS per Polycom fix will be targetted for 4.2 which is scheduled for release at the end of November.
Reference SR # 1-606780121
Issue resolved in upcomming Iron Man release for Group Series Jira reference GS-17384 (Can see only the speaker on GS EP) (Escalation for visibility)