It happens regularly every few weeks to months. No one knows why as the FFN admins have never provided an explanation. It should resolve itself in a few days. And usually only applies to new reviews when the issue happens. Guest reviews and member-posted reviews included.
You can read about this happening to other users via the
FFNet Help Desk Forum. Lots of peeps tend to post that they're experiencing the same thing too.
A thread is here:
www.fanfiction.net/topic/20103/159172250/1/Reviews-not-posting-or-showing
It seems some email alerts for the reviews are truncated along with other issues.
~ Pyre