I am sorry to hear you are not able to download your group messages. I can help you get this resolved!
Group messages require a cellular data connection. Please try turning Wi-Fi off, mobile data on, and check if you have a 4G/LTE signal. If you do, try and download the group messages again. Older messages may need to be resent.
I also recommend using our Troubleshoot & Resolve Tool. Select your make and model > Messaging > I Can't Send/Receive Messages > Group Messaging. This will provide personalized troubleshooting tailored to your device.
If you are still experiencing issues, please let us know. We are eager to get this resolved!
Jonathan, AT&T Community Specialist
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*I am an AT&T employee, and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.
I found the solution for MMS messaging issues related to the Samsung Galaxy S6 and S7 series phones. The APN settings that are listed on the website are reversed. The APN type settings should be as follows
This slight change will allow MMS to come through.. 05/20/18