Do you mean that if you get incoming, you get a ping unless it's a reply to an earlier text? That would be really weird.
Or do you mean that you don't get a ping for any incoming texts?
If the latter, go to Settings / Sound and Notification /Notification sound.
Having put my original post, I've been notified each time my friend replied, although earlier on I didn't get notified.
I've noticed it before . It's when I have texted someone and when they reply my phone doesn't ping. Unless of course it's like today when it has done!!!
I think I will go back to bed!!!
//I think I will go back to bed//
Good idea, but remember that Samsung phones have their volume controls opposite the on/off button, so it's dead easy to accidentally alter your volume when waking your phone. :-)