Instagram is constantly improving their SPAM filters and it is getting harder and harder to post SPAMmy images there. And Images that “contain a lot of text, including a number of links to other locations on my website” are indeed SPAMmy from Insgram’s point of view. If it worked several years ago it doesn’t mean that it will work today. Several months ago nobody even heard about “Unknown Server Error” errors.
And, yes, Facebook acquisition of Instagram as well as all recent privacy issues played a hard role there.