Interesting to see this happen, my thought has always been its freeze dried food, it lasts forever pretty much.
This summer I had one that was slightly past its expiry date (its freeze dried food it lasts forever was the thought). I honestly could not finish it, it had an incredibly strong chemical after taste and gave me cramps and stomach ache almost instantly, luckily I didn't have any V&D symptoms, but it took most of the next day to feel right again.
The only thing I would put it down to is that it was living in our camper on and off for a year or so - maybe the hot/cold fluctuations got to it?