So I’ve been having this problem since my iPhone 6 which carried to my iPhone X. So I don’t thing it’s the phone. I talked to Apple support and AT&T and got pushed back and forth...ugh. Anyway but I did the resetting of network, turned on and off phone, reboot, etc, theses methods all work but only temporarily. I also tried this method from a suggestion from ATT. “Settings/Message and toggle off in this order: group mms, mms, send as sms, then iMessage. The back to setting: tap on cellular data the turn off phone. Wait fir a few minutes then turn on phone and toggle everything back on in reverse order. This method seems to work the longest but eventually the problem returns. So got back on the phone with ATT and Apple again for an hour each and found no solution from them but did find out that when there’s a android in a group of iPhones, it turns every single message exchanged in that group to a SMS (so we better make sure we have enough data package to cover or always in WIFI). So I started thinking maybe something in the setting in the background from upgrading to newer iPhones everywhere might have caught some sort issue. So what I did is 1. Did a network reset. 2. Reset all settings (resets all settings to factory but keeping your data), 3. Reset location and privacy. 4. Backed up my iPhone to my iTunes (this backed up my data with all the settings in manufacture default. 4. Restored my phone on iTunes buy downloading the newest iOS so my phone is now in the state when I first opened the box. 5. Once it finished restoring to a new phone with nothing on it, I selected restore from the backup I just did with the factory default settings. 6. Then of course I had to go back and redo my settings to the way I like (don’t forget to turn on mms and group during the process). It was a pain in the *** but I think I’ve been doing ok. I text a sep text to a person in the group and ask her if there were any texts sent that I didn’t get. So far I seem to be ok and it’s been two days. Where as all the methods before problems return sooner.
