Here’s a weird one for you, can a PC with Lucky reroll an enemy’s initial Grapple check? We are torn as Lucky can reroll attack rolls. but grapple is a special attack so we are unsure as to if it's affected

— Penguin (@Thepenguin9) September 4, 2017

With the Lucky feat, you can affect only an enemy's attack roll. It's no good against an ability check.

— Jeremy Crawford (@JeremyECrawford) September 5, 2017