DIAGNOSIS The auto-off timer is likely stuck. This function is controlled by a simple internal timer circuit, not connected to the brew cycle. It's a known failure point.
FIX First, perform a hard reset. Unplug the machine from the wall for at least 2 minutes. Plug it back in, but do not start a brew cycle. Just turn on the power/warm switch. Let it sit for the 2-hour auto-off period and see if it turns off. Sometimes this resets the logic.
IF THAT DIDN'T WORK If it still stays on indefinitely, the timer chip on the control board has probably failed. There's no user-serviceable fix for that.
HEADS UP Since this is a fire safety feature, if the auto-off stops working, you should make a habit of unplugging the machine manually when you're done using it. Don't rely on it or leave it plugged in unattended.