Nothing is "really" wrong with the K&N, they do sort of filter, not as well as paper, but the issue in question is related to the hot wire MAF and contamination. Many owners cheerfully toss their K&N into the trash after replacing a MAF.
Two caveats;
MAF deterioration is gradual and not easy to detect until engine management issues are causing obvious problems unless you carefully track fuel consumption.
Most of the damage is due to over oiling the filter.