I thought it began when Luffy found out the right mr 3 out of the wax clones

Then of course Enel and the little girl in skypeia

I read your comment wrong. My bad

I believe the reason why smoker was hit because he wasn't expecting luffy to be behind. Logia users must be prepare to turn into their form which he didnt

He isn’t always Smoke because he didn’t expect Luffy to hit him so he didn’t turn into Smoke, watch the 4th movie and you would know

The reason is basically smoker didn’t prepare to turn on his logia form. He didn’t luffy to come out from behind him. Ace was using fire but he wasn’t prepared to turn on his logia form fully as he was not expecting that. Logia users won’t always be in their logia forms as one time a girl with an ice cream bumped into smoker’s leg

PIot Induced Stupidity

If Logias were their 24-hour elements, they wouldn't need to eat and they wouldn't have physiological needs. We know that Logias eat and have physiological needs. Soon Smoker was simply not active in his element at that moment. Crocodile maybe was, it could have been a different context where he felt threatened and transformed just in case.

I think its because he didn't expect Luffy to come flying at him and since logia users aren't always their elements i don't see it as a plot hole.

I don't know your supposed to use Haki to hit someone with a logia

I think that when u have a logia, its a choice wether you want it 24/7 or not. It could depend on the situation of the logia user ie, crocodile is constantly going to be hunted down by royals etc but smokeeer was just talking so he didnt need it on. or like when kizaru was exploded by apoo depending the situation he was in battle which made him be on guard