I've noticed this the last couple weeks, thinking friends had been dormant but then checking their pages to stalk and seeing they had posted reviews. With time zone differences I just thought I missed them; I do try to do a scroll down for the last 24hrs when I glance at my feed to try and not miss anything. Alas, it's just GRs deciding that certain people I've chosen to be friends with aren't important and simply not put their reviews on my newsfeed.
Good news, though! They say you can get emails of everyone's reviews! Oh how delightfully email flooding. I mean, why would I want to simply scroll my newsfeed for that?