Instagram is now loading user feeds with recommended posts it thinks you might want to see based on accounts you follow. More specifically, the recommendations are based on the likes of those accounts you follow. What this means is that if one of the accounts you follow likes a post from an account you don't follow, Instagram can end up tossing that post in your feed now so you see it too. To some this might be a welcomed new change as it will potentially give them a new way to discover content they might actually like, and it makes sense as it would stand to reason that pages followed by the accounts you follow might also be accounts you would be interested in.
Not everyone is likely to want this change though. There appears to be a mounting number of users complaining about the changes via Twitter, stating that they follow the accounts they follow for a reason and if they wanted to see those posts which are being recommended to them, they'd follow those accounts as well.
When recommended posts show up in your home feed they will apparently come in groupings of three to five, and will be labeled with a "recommended for you" tag so that it's clear these aren't actually part of the list of accounts you follow which normally show up in your feed. It's also not possible to completely disable the recommendations, so users who don't particularly care for them will unfortunately be stuck with seeing these posts in their feeds from time to time as they will surface after you've viewed all the normal posts in your feed from the accounts you follow. That said, it is possible to temporarily hide the Recommended For You section so you can at least minimize the amount of times you have to scroll through posts and content which you might not typically see. To do this, if you choose to hide recommended posts, all you have to do is tap the three dots in the top right corner of the recommended section, and the option to hide them will be listed in there. It's also worth noting that this appears to be rolling out to users still so it's possible not all users will see them yet.