I have seen this problem with really long hdmi cables, or poor hdmi cables, it’s a data rate issue.
Is the problem on Mi Box S, on Netflix, or on my TV?
Only time I saw this consistantly was on a crappy internet connection. Streaming netflic from my Roku which was sat next to the hub byb the way!
I've since moved from Sky to Virgin internet and the issue hasn't occurred since. In my experience seeing all that noise on the screen seemed to be associated with my internet, not a device.
See if your TV settings have any type of sharpening, de-noise, or upscaling going on. And turn it off. That’s what it looks like to me, I could be wrong. You may need to read the TV manual because tv companies have different names for some of that stuff. It also might just be your internet, but those white specks are unusual.
Episode "New York, I Love You" from Master of None looks like it's in 240p on my Mi Box S. Any other episode plays fine, including the same bad episode when using my notebook.
That looks like an HDMI problem.