Guys this is not torque related. The system senses an engine fail (and displays ENG FAIL on the CAD) when it senses less than 50% N1. When this occurs it changes to the OEI limits. That said the engine is still running but only just.
Try winding off the twist grip next time you shutdown (make sure you go the correct way) you will see it happen before your very eyes.
A lot happens at or less than 50% N1. ENG FAIL caution, start cycle terminates and Fire bottle discharges if EMER OFF Sw pressed.