I wonder for the one with terrible recommendations if I fell into a particular failure spiral: YouTube tried to give me some new stuff for a period, but I happened to not like any of it. The AI noted I was just clicking suggestions from my subscriptions. It eventually tried different recommendations. I didn't like those either, and clicked videos I'd seen before from my subscriptions. Eventually the AI decided I only like watching videos for channels I'm subscribed to, and now doesn't recommend me stuff outside of that. Even when I branch out into a new area, it no longer suggests related channels or anything like that.
It works great when it types out phrases as I swype and I go back and edit in whatever jokes, memes, or 10 dollar words I want to include. It starts to suck when it starts trying to include those into its predictions.
There's like a sweet spot of machine learning beyond which the machine gets more annoying than helpful.
I remember that Spotify actually had pretty good recommendations when I first started using it at the start of this year, because I had only listened to the songs I actually liked so far. But now I'm lucky if I find one decent song out of a hundred recommended ones.