NGK spark plugs breaking.
That is the recommended longer plug, to get the plug closer to the combustion area. Unless you have shaved your cylinder head an exuberant amount, hitting the piston isn't the problem. If you were hitting pistons, you would know it.
My recommendation would be to thoroughly inspect the plug, before the install. And to be careful with the plugs when installing. I use the same plug, and have never had any issues. And my cylinder head is shaved .100