It is not the carrier. It is the phone. This only happens on the Samsung phones. All other phones i have tried it does not do this popup message. But, If you go into Messages/Settings/More settings/Multimedia messages/Group conversation. If you uncheck that the messages will can still be sent where it looks like a group but is actually individual messages and replies all come back separate. If someone comes up with a cure for this please let me know. A good work around is using the app Textra. I works very similar to original app but has much more customization.
... View more