Game not smooth (micro lag) at low fps (30)

Hello everyone!
I’m making a slide game constantly from top to bottom screen, so the idealy all nodes will add to 1 container node, which will be slide from top to the bottom,
the game really smooth on high-end device which alway running with 60fps.
Howerver when the game run on iPhone in low Power mode, the game just run with 30 fps (i think it come from os system, checked on other web game run on it in this mode).
I just make a simple move on update function:
like ,
this.gameContainer.y -= this_speed * dt.
or this.gameContainer.setPossition(newPos),
but the game will not smooth.

Also tried with cc.moveTo, cc.tween to move the object but the sittuation are not changed.
And it same when we check on window browser with limit fps to 30.

I don’t know if any one get same problem before and already solved it.
Somebody can give me a hand please, or any advise are welcome.
Thank you!!

I didn’t tested and didn’t check if this is possible before post, only talking by gamer experience, but maybe the problem is not be 30fps, but not being a constant fps, if it goes 30, 35, 30, 35, it will be weird. Try lock at 30 fps, see if the problem persists.