Wtf happened to my oil??

Alright guys, hoping someone can help me out. . .Pen on the right is obviously how the oil should look, but any idea what happened to the cartridge on the left?? Can a pen burn

the oil?

Thinking back to my resin and kief days (not my best 🤣), I still plan on finishing that cartridge on a different pen, but just curious if anyone has had this happened and/or knows why. . .🙃