Quote from CME
CME Group says no trading error this morning.
CME Group Stop Logic was triggered at 10:16 a.m. ET for 10 seconds in our Henry Hub Natural Gas futures contract on Globex," said Chris Grams, a spokesman in Chicago in an email.
The "Stop Logic" mechanism sets off a momentary pause in trading, which lasts between 5 and 20 seconds, "to prevent excessive price movements from cascading stop price orders" and allowing the market to regain its equilibrium.