I will never understand why Youtube's notification system is so fucked, you'd think it'd be an easy task for it to show you videos from the people you're subbed to.
i had that same issue. TeamYouTube replied to my initial message telling me to clear my cache and asking if it showed up on another device, and when i gave them an update (it wasn't figured out yet) they went silent. i wonder if they're actually trying to fix it :/