https://techcrunch.com/2019/01/28/apple-disables-group-calling-in-facetime/

Apple has disabled the group calling feature within its FaceTime calling service while it works on a patch to fix a nasty bug that allows eavesdropping.

Apple’s status page shows that group calling via FaceTime is “temporarily unavailable” — that’s a stop-gap move while the company to deliver a more permanent fix to the problem this week. We were unable to set up a group call when we tried, having earlier been able to do and replicate the issue.