As of yesterday or the day before I now do see purple twitch logo images are being generated sometimes. I’m assuming those are the generated ones you’re referring to.
Agree, it seems images are now loading much faster.
Personally, I’m ok with the images not updating frequently as I now have my own preview caching in place, so I’m only loading each stream preview image once, the first time I load a user’s followed live streams and for every stream that goes live after that. Works like a charm 