A recent update to (Android) Messages appears to have reset a setting for many folks that causes group messages to go out as multiple SMS messages rather than as one MMS. You may see the error message: “This Conversation is now a mass text. Each recipient will get an SMS message from you. Replies will appear in individual conversations.”
The fix for this issue is easy:
- Open Messages
- Click the three stacked dots on the top right (on the main page where all conversations are shown)
- Select Settings, then Advanced
- The top item in the Advanced menu is the Group Message behavior. Tap it and change it to “Send an MMS reply to all recipients (group MMS)”.