Since the beginning of September my phone has been giving me issues with both receiving as well as sending messages. On the receiving side it seems to not display messages the other members of the group have received the message. And less frequently people are saying they are not getting my message so it shows up in my conversation history as being sent.
I primarily use GO SMS Pro as my messaging app but even from within Samsung messaging app I can see that I've missed some messages
I've also had the same issue of not receiving messages in both group and individual conversations. I ended up switching from the Google Messages app to the native Samsung Messages app and it seems to be working now.