There's no such thing as group SMS. Your phone either sends multiple SMS messages, or uses something else than SMS (usually MMS). I'm talking about SMS specific

There's no such thing as group SMS. Your phone either sends multiple SMS messages, or uses something else than SMS (usually MMS). I'm talking about SMS specifically, as CSM chunks aren't relevant to anything else. My assumption is that iOS somehow manages to lose some SMS messages when sent in rapid succession more often than it would happen for usual reasons.