I haven't gotten any notification for the past 16 hours. However I have spoted an article, a model and a comment published during that time span, I should have gotten a notification for. My conclusion is that notifications are not working since then. This was also confirmed by another user on an article comment. If you encountered the same please leave a comment. I already filed a support ticket for this and will update this article, if I get a response. If you wanted to publish anything today, you probably should refrain from it, since none of your followers will get notified.
update (20.05 02:20 UTC): I got a response from support:
"Thanks for the follow-up. The 16-hour gap you described lines up with a known infrastructure outage on our end (it started around 01:00 AM Central on May 19 / 06:56 UTC). One of our internal nodes that handles notification routing went down, which is why nothing came through for that stretch even though articles and models were being published in the meantime.
The infrastructure issue has been resolved and notifications are flowing normally again. The notifications that should have fired during the outage window can't be replayed, so any events from that timeframe are not recoverable on our end. To catch up on what you missed, your followed creators' profiles and the model / article pages directly are the most reliable places to look.
Closing this and the earlier ticket out as resolved."
Funnily I have just received a notification for the comment made 12 hours ago and for the article and the model mentioned above, so at least some notifications are recovered.
update (20.05 17:30 UTC): As much as I can tell all notifications that were triggered during the notification delivery outage have been restored. If you think otherwise, please leave a comment.