Kennen's W's passive does not apply to 3 enemy's after you bought Runaan's Hurricane.

Runaan's Hurricane's Unique Passive is - WIND'S FURY: When Basic attacking, bolts are fired at up to 2 enemies near the target, each dealing 25% AD physical damage. Bolts can critically strike and apply on-hit effects.

Kennen's W's Passive is a on hit affect and it doesn't apply to 3 enemy, but only 1.

Also Kennen's W's passive does not apply another stack of mark of the store when you have 6 stacks of Guinsoo's Rageblade. When you have 6 stacks it only applies 1 Stack of Mark of the store when Guinsoo's Rageblade passive is - UNIQUE – GUINSOO'S RAGE: Every other basic attack will trigger on-hit effects an additional time.

This is a really annoying bug for all the Hybrid and adc Kennen players. Please fix this bug soon.