I also just discovered the lack of group messaging in the stock SMS app. It seems strange that LG would omit such a basic feature. I'm now on a quest to find a solution. This is my wife's phone, and she is not a "techie", so I need to keep the solution simple.
Tried QKSMS, but it didn't seem to handle group MMS correctly.
Tried Textra, and it seems to handle group MMS ok, but the free version displays ads.
Tried Google Messenger, with is nice and simple and seems to handle group MMS ok, but it doesn't show the unread message count (notification badge) on the app icon. I found an app called Notifyer which can add a notification badge to the icon, but it is uses a widget to do so, so you can't put the icon with badge in the dock (the row of icons a that are locked to the bottom of the home screen).
I have read that some 3rd party launchers like Nova allow widgets in the dock, but I don't really want to switch launchers.
Has anyone else come across any other solutions?
For now I'm using Google Messenger with Notifyer, and putting the widget on the main home screen just above the dock. Note that I also had to fiddle with the Notifyer settings to increase the size of the widget to more closely match the other home screen icons.