We have had some customers with some problem with PLA and I guess that it can't be wrong to try to help with some advice regarding the storage of PLA!
PLA is naturally sensitive to MOISTURE and HEAT!
If you have a rolls of PLA close to an open fire it will be destroyed, best is to keep it dry and in shade or darkness. PLA is basically a milky acid derived from Corn or other cereal. That makes it very thirsty, PLA want to suck up moisture.
Keeping it dry and cool is a good idea.
Heat as upon all products of this kind will melt, deform and dry out the PLA so it will be difficult to remelt through the extruder and also brittle ( easy to break ) the general print will also suffer since the PLA looses a bit of it's flow factor.
These are some of the drawbacks for using a VERY naturally friendly and non toxic plastic in our printers. I can also imagine that pests like mice and other pests would like a nibble on PLA. PLA of medical purity is what the medics use inside your body for thread when operating and sewing wounds. This capacity for breakdown by living tissue as well as water is one thing we must learn to live with when it concerns a material like PLA.