This might be the case where you are inputting an extra notation on the PS4 Dpad (Since this is the only controller we can use.) Basically when you go to training mode, look at the bottom and you can notice that after hitting [3P] you are also hitting 6 again. Controller's fault there.
So basically there may be instances where you know for sure you hit it at the same time, but because of the extra buffering..it comes out wrong still..It may look like this 3P > [36P] when you are actually hitting 3P but you can't get that right diagonal in because the Dpad direction is blocking it.