Looking at the latest page for really busy fandoms like e.g. Harry Potter shows the results - the most recent story showing on the first page was posted on the 30th - there's one story above it, showing as last updated on May 30th. What I think happened with that one is that it was actually updated after the problem started to occur, but the update isn't showing.
So if you're posting to fanfiction.net, or read stories there, I'd strongly suggest looking for alternatives.
Update, Thursday 00.02 AM, looks like it started working again some time in the last couple of hours, stories are updating.
later - some are, some aren't. REALLY annoying.
Also posted at https://ffutures.dreamwidth.org/2214119.html, where there are comments. Please comment here or there using OpenID.