As noted in the numerous reports filed by pilots on very similar incidents, they simply turned off the autopilot.
The inherent difference here is the use and dependence on the AP.
As noted by one pilot, he usually doesnt engage it on until FL10, when he did, the ac began to squawk. Simply turning it off returned the ac to normal.
Perhaps this is why there are not as many incidents in more congested airspace, the ac is actually being flown. There are very few RNAV DEP.