Have read the same, the thicker electrodes of copper (actually nickel on the business end, even iridiums have a copper core) erode much faster with the high voltages in modern ignition systems, leading to misfire and other issues.
Great for an older none boosted engine running a single coil and leads from a dizzy etc.
I had 2 fresh sets of NGK copper nickel plugs die on the dyno in my old Subaru, anything over 10psi boost and they'd start breaking up and misfiring, swapped them out for a set of platinums from memory and then it was mint even pushing 22psi into it.