missing some messages in a group message

My wife and I both have 5s, running ios 8.3 (her) and 8.4 (me). We can text any single person, and not miss any texts. When we do a group text, we don't get all of the messages others do.

For example, today, we had a group text with our son (android user). I lost the general idea of the conversation, and when I checked my wife's phone, she has sent a message that our son recieved but I never did.

We did not jail break our phones. We are the original owners.

Before I upgraded to 8.4 last weekend, I did "Erase All Content and Settings" and then restored from backup, so resetting the phone is not a solution.