[ChristianTroy]

It's something already noticed if you were using the proper 23.976 mode with Netflix, cannot say why, you don't have any control over this, it's the black box like fritsch said
Before you never experienced it because Netflix was executed at 24fps at best (if you had selected a 24hz resolution or you were using refresh rate switcher)

edit: name a video where you can see it (Netflix possibly), right now I'm trying a bunch of US tv serie that are 23.976 and I cannot see it