Have you checked what your feed settings are?  On the web, you can click on your profile picture, then on “display preferences” on the left, then scroll down to “feed ordering”.  In the app, click on your profile picture, click on the little gear in the top right corner, and then scroll down to “feed ordering”.  It can be set to “Latest Activities” or “Personalized”.  If set to personalized, it will serve up activities it “thinks” you would like to see first and not necessarily in the chronological order.