In Febuary of this year, facebook.com made some changes to their website settings and you might not have noticed it yet but you might check this article.
Facebook changed the options in its news feed settings so users either “Show posts from: friends and Pages you interact with the most” or from “all of your friends and Pages.” Some users have unknowingly been defaulted to the first option, causing lot of content to be hidden from them without their knowledge.
It’s not exactly clear what determines which default users receive, though newer accounts appear more likely to only be seeing content from a subset of friends. Previously users could select exactly how many of their friends they saw posts from.