If stored in unsealed bulk, high humidity can make it condense into a solid and become unusable in bulk, which may have happened here if stored in a bulk storage elevator. Then it just sits becoming more unstable.
It doesn’t even have to be high humidity. I have seen it caked up in storage silos in NV. The desert of Nevada doesn’t get much dryer than that in the summer.
What’s crazy is that I have never seen places go to any effort to protect it from moisture. Not in transit nor in storage.