No plausible mechanism for a measurement error or artifact has been found, though it's still possible.
Given the circumstances, a measurement error or artefact is absolutely plausible. I posted a hires plot of the ambient temperature measurements during the occurrence of "the signal" at the time on ecatnews. Here it is again: https://postimg.org/image/nza0n6nub/full/
I wouldn't trust any measurement done during those hours with any instrument in that room. Looks like static discharge against a ground leak to me. The other TCs seemed to be similarly confused.