Why does my "Hairstory New Wash" have a rancid smell in glass container

I use Hairstory New Wash for my hair. A few months ago, I bought a glass and metal dispenser to squeeze out my refills into. I recently noticed that instead of a pleasant smell, there is a rancid / acidic smell coming from cowash inside and pumped out of the container. I wonder if this is because I would just layer a new refill on top of the old refill over and over. But the same refill packets still smell perfectly fine inside, even after months of being on the side & having been opened before. Any ideas why the glass container now has an expired cowash, or is my guess correct?