I don't know what the system is and I don't know why it exists, but it's stupid. Regardless of what someone originally subscribed for, why limit the notifications down to less than 1% simply because a clearly faulty system believes it picked up on something somewhat unrelated to what the channel usually shows? What is this supposed to accomplish? When someone subscribes, they want to be notified when the channel has a new video uploaded. Why remove the one and only function of that? What's the point of even having people subscribe at that point?
There's a channel I have that has about 500 subscribers that had a video uploaded to it today. Within hours, it reached about 600 views. The channel with over 50,000 subscribers' video took 4 days to reach that. How innovative.
YouTube's just been a sinking ship for so many reasons the past few years, but unfortunately this, to me, is just a final nail in the coffin. Sadly, there currently aren't any realistic websites that provide the same services YouTube does. Nobody is or even knows about any of the site's equivalents. There's nowhere else to go.
It's a shame. I want to be doing this animating/directing stuff for real one day, and seeing the way things are now, that day couldn't come a moment too soon. Here's hoping.