I made a popular recipe Sinnamon Cookie 8 months ago. Used some with no problem, but then put it aside until recently. It’s quite a bit darker after 8 months, but otherwise looks crystal clear. Now, when using it in a VandyVape Beserker tank, it is leaving a nasty looking black residue in the bell chimney. I’ve run several other juices through that tank and never see any residue. Vaping MTL at about 8 watts on a 1.8 ohm coil.
Any idea what causes the residue?