I suspect that your Anaerobic Threshold test was not accurate. Maybe you were tired??
Are you collecting the HR data with a chest strap or off a wrist monitor. Wrist monitors are inaccurate and read high.
Being able to go for an hour at 170 and see less than 5% decoupling would indicate 170 is your aerobic threshold. You’re right that an AeT/Ant difference of 5% is very unusually high.
This decoupling test has very high reliability. In our use it seems accurate for well over 90% of the people who use it. But it is not the gold standard and you something is strange then a gas exchange test like they do at CU will dispel any questions.