Thanks for this concrete and comprehensive visualization.
It must've been the Spheroid. I assume one side of the coil shorted somehow. My only explanation for why it stopped happening is the heat must've either 'jolted' the coil back in place, or built up a nice protection of carbon so it wouldn't happen again.
I usually wrap my coils around a jeweler's screwdriver first, and then thread cotton into the coil afterwards. This time, however, I wrapped directly around some ekowool, and I must've done a shoddy job keeping the wire off the thumb nuts. If it's not my coil, then it might be the positive insulator ring, which doesn't seem as snug as it once was. There are also rubber rings underneath the thumb nuts that look a bit overcompressed. I think I'm going to order some replacement parts.
Considering I'm using a SS drip tip, I would prefer not to experience this fault through my lips.