Apple has just issued an update to iOS (version 12.1.4) and macOS (10.14.3 Supplemental) to fix the notorious FaceTime bug.
Apple also took this opportunity to fix a couple of other security bugs.
Make sure you update today before Apple re-enable the Group FaceTime functionality. Otherwise, you run the risk of being eavesdropped!
Urgent iOS & macOS update to fix FaceTime bug