I was following is thread as I had this issue too.
Last night I had all 3 phones updated iOS12.1 and it has fixed this issue. 😀
[edit]
...just read the above replies! See you all knew that! 😕
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Having the exact same experience here. Without question, this issue began when I “upgraded” to iOS12. This issue has been devastating and needs to be resolved ASAP. I depend upon iMessage and can no longer trust/depend on the tool to send messages to the proper person. In the same way, I cannot be sure from whom texts are actually being sent.
I was following is thread as I had this issue too.
Last night I had all 3 phones updated iOS12.1 and it has fixed this issue. 😀
[edit]
...just read the above replies! See you all knew that! 😕
It doesn't change the fact that using the same AppleID for multiple users will cause lots of strange behavior and lots of problems and is something you should never do.
Update the device to iOS 12.1. That was supposed to fix the combining of the threads.
Update your IOS to 12.1.
Still doing it, everything is updated!!!
Everything is updated, worked for an hour, then combined again!!!
Are your parents sharing an Apple ID? If they are, they need to update to iOS 12.1 as well.
Any fix yet???? This is driving me nuts!!!
Did they tell you how to fix this? When I call apple support they have never heard of it
The answer has been given several times in this thread.
This is happening to me and my husband with our daughters phone. We all have a serrated apple id
Did any of you EVER share an Apple ID?
I had to create a separate Apple ID.
This and other bad things will happen until you stop sharing an Apple ID.
I guess you haven't read any of the thread you posted to. You might find it enlightening.
Why is iMessage combining two contacts into one thread. I can only text back the last one that messaged me. This started with iOS 12