When using Messages on either your iPhone, iPad, or Mac, you might run into an issue where conversations will become split into multiple threads, where at times messages will arrive in one thread and at other times they may end up in the other. This can not only be a little cluttering to your organization in Messages, but can be confusing since you might not know what thread to use when attempting to connect with someone.
This problem can sometimes be fixed by closing the threads and starting your conversation freshly, though if you do this the conversations will likely split again in the future. In addition, doing this may lose any prior conversation content, which you might want to keep around.
This issue happens largely for two reasons: Your contacts are out of sync between your devices, and you have errors or conflicts with the configuration of your contacts. Sometimes fixing this can be a little involved, but once done your split Messages conversations should combine again.
1. Ensure your Contact cards are complete
iMessage can communicate using any e-mail address or phone number associated with your contacts, so be sure you have all of these set up. If you only have one e-mail address for your contact, then you might be messaging your contact using a phone number, or another e-mail address, which may have Messages think these are separate contacts. When you edit your contact, you can click the plus buttons to add more phone number and e-mail address fields, if needed.
2. Ensure your contacts are properly synced between your devices
Apple supports many options for sharing contacts between your devices. You can directly sync them using iTunes, or you can keep them in iCloud, or you can use a number of other online services such as Yahoo, Google, and Facebook to manage your contacts. Regardless of what you use, if you have contacts stored in one of these services and this service is not configured on your other devices, then conversations may not be properly assigned to the contact.
3. Check for and remove duplicate contacts
You can have multiple contact cards with the same information on it (since after all people may have the same names), so it is possible you have a person’s e-mail in one contact card, with his or her phone number in another contact card. If so, consolidate these into one card to prevent confusion in Mail. To help with this, you can use the “Look For Duplicates…” option in the Card menu of the Contacts program.
4. Delete and re-create contacts, if necessary
If a contact’s card appears to be complete, but for some reason conversations with this contact are being split up, then you might try copying down the contact’s information, or exporting the contact as a vCard (done in the File menu), and then re-importing the contact or creating a new entry for him or her.
5. Use iCloud to manage contacts
While your Mac can store contacts on it along with using contacts from various online services, to help avoid conflicts that can lead to conversation splitting, try consolidating your contacts in one service, and preferably use iCloud since it is Apple’s most compatible service across its devices. You can do this easily by going to the “On This Mac” section in the Contacts program and selecting all items (press Command-A to highlight them all). Then drag them onto the iCloud section, and they should now all import to iCloud. You can then delete the ones on your Mac.
Once all of these options are accounted for and your contacts are properly set up, quit and re-launch Messages, or optionally restart your iOS and Mac OS devices to have Messages properly load and assign conversations to your contacts.
None of these fixed the issue.
Seems like it’s because of new updates/new phones. I’ve been in a continuous group text for years now, it has been fine until recently when some of us either updated their IOS or got a new version of the iPhone.