Graves + Ludens

it procs on spells, not on auto attacks. ez Q is an auto attack.

Could have been overlooked, but as i just told someone else, Ez Q deals physical damage, not magic. That is why it doesn't proc Luden's Echo.

This is intended. As said before, Luden's Echo will proc on any spell, and it doesn't matter what type of damage the spell does. It can be magic, physical, or even true damage.

However, Ezreal's Q is treated as an auto attack, so whatever an auto attack can and cannot proc will also apply to Ezreal's Q. And since auto attacks cannot proc Luden's Echo, neither can Ezreal's Q.