posts and likes not showing

I think it seems to be intermittent but some friends posts or likes do not show up when I go to their page. Or in my news feed. Its the same friends sometimes so its not like they are constantly changing settings. It also seems like I can see if they post are mutual friends.

Do they like this stuff on external websites (with the "Like" button) or on Facebook itself?

It can be liking someones post or page. It can just be they write on someones wall.