I have never managed to catch Facebook out, although I have tried once or twice, until today when I posted a link to Laudae Finem and then on a hunch I contacted an alt political friend and got him to look at my homepage. And what do you know, the last post he could see on my homepage was from him even though there are ten posts, seven of which are political, after his post to me. All seven political posts would have interested him, so what happened? Why can't he see them? Or, why does Facebook show them to me but not to him. The last page I posted had been shared with Facebook more than 6000 times if you are to believe the little share button so it isn't unpopular.
Another way to look at it is that Facebook is a company with shareholders and must make money. One way to make that money is to advertise, another way is to change peoples feeds to point them toward ways of Facebook making money, and the last way is to have and maintain the largest market share so no-one can upset your throne and stop you making money. This doesn't fulfil the first proposition as nothing was advertised more or less than normal. It doesn't fulfil the second proposition in that not having anything on my page didn't point my friend anywhere except away from the page as nothing was happening. It doesn't fulfil the third proposition as the way they maintain market share is by encouraging people to interact on their site.
The only other thing I can think is a reversal of the second proposition. Facebook changed its feed (eg; the view of my homepage to my friend) in order to make money by not showing things to people and that is enough to me nervous.........