Why do I get two message threads for one group message in iOS 8?
Some iPhone users are reporting a bug in iOS 8 that causes them to receive two messages for one group thread. For example, you have a group titled "Soccer Moms" with six contacts assigned to that group. Five of those user's texts are delivered via the group thread but 1 is delivered via a separate thread / text window. This is just one of many confusing problems plaguing Apple's new iOS 8 group messaging features. Some users are having trouble changing the name of a group text and using the group messaging feature altogether.
Most of the problems with the new group messaging features stem from one member of the group not using and iOS device. For example, you can't add or delete a person from an existing group message if they're using an Android phone. However, this does not seem to be the case with users receiving two messages for one group message. Hopefully it is just a bug that Apple will fix with a future update. Let us know if the comments below if you're experiencing this problem or know the cause.