So, I have a buddy that purchased an S4 and up until now hasn't had any issues with group text.. He uses the stock messaging client and is having two issues: 1). Some messages don't come through 2). Text comes in as "Click to download MMS" followed by "Can't download MMS" or "MMS is no longer available". I personally have never had issues with MMS regardless of client and I've used stock, Textra and now Hangouts. I had him switch to Hangouts, but that just made things worse so we reverted to stock.