A 14 year old teen discovered that if he re-added himself to a group conversation, he could hear conversations even before primary party picked up on phone.  While this is not a logical or normal action, this bug can compromise security & is currently being fixed.

https://www.zdnet.com/article/you-may-want-to-disable-apple-facetime-this-week-callers-can-listen-and-view-remotely-without-your-consent/

https://www.zdnet.com/article/apple-gets-egg-all-over-its-facetime/

The bug that allows people to listen in to other people’s phones and even see video hits Apple where it truly hurts — in its protestations of privacy protection.  A bug on the ever-popular video-chat mechanism allows people to listen in on other people’s daily lives and even watch them doing things they likely wouldn’t want anyone to watch. Especially someone with whom they might occasionally FaceTime.   Naturally, Apple has already declared it is issuing a fix.