I found this too, so much that I think it contributed to why I've stopped using Instagram much - along with feed changes etc. In Instagram's defence, they all had a slight relation to the content I'm interested in and usually many more likes than other posts (presumably half-naked pictures are appreciated) - this would probably rank the post higher and Instagram would try to show it to more people.
Why, oh why, can't they just show a feed of the people I follow in chronological order at the post I was looking at last time I was on the App.