I have a friend who worked as a food scientist for Kraft and later Mondelez. One day were talking one day about how shelf-stable foods had suddenly gone through a fairly drastic shift in flavor. She told me a lot of that was a result of the banning of artificial trans fats. My guilty pleasure used to be Wheat Thins (hers was warm Oreos straight off the production line) until one day somewhere between 2013 and 2015 they began to taste like a crappier version of salted fried cardboard. I was sure this was a result of cost cutting and preparation to spin off Kraft's snack food division into Mondelez but she assured me that while that may have had something to do with it the major driving force was the shift to fats other than those based on artificial trans fats.

I can't say for sure if Pop Tarts suffered a similar fate but I'd say there's a pretty good chance.