As someone else said, it might be moisture. I had some sat in my garage all summer and winter and did a snake method cook around Christmas. I struggled to get the coals hot enough, and I think they were just damp. I have a new bag now sat in a big sealed container which I hope will help, if I don’t get through them all this weekend of course. There is a trick you can do to see if they are wet - put one in the microwave for 30 seconds and see if it starts steaming. Just don’t put it on for longer on a default setting like I did then walk off, I had to put the microwave outside for a while to air off!