You didn't ask me, but I'm on my 3rd round with Tomahawk and haven't had any problems cloning it...so far. To be honest, I'm kinda just waiting for it to happen though.
GG4 has many reports of "dudding" and peeps have had very poor rooting rates. You might have a GG dom plant? If your JP is rooting fine in the same cloner this might be the cause.
For more info check ICMag or possibly here. I think I read
@HydroRed had some issues with his gg4 clone. Sometimes its due to the health of the mother and sometimes its just a branch or two that duds.
There's a lot of theories surrounding it and those threads can give you a more in depth answer than I can.
Hope this helps