Auto-dry on your model works by temperature, controlled by the thermostats on the blower housing. The timer does not run while the heating source (electric element or gas burner) is active ... that is, when the exhaust air (drum temp) is less than the target operating temperature.

When the target temp is reached, the element turns off and the timer turns on ... until the temp drops enough to trigger the heat source back on. And so it goes, cycling between heat-on/timer-off and heat-off/timer-on until the "time" runs out to Off.

Per parts diagrams your machine has two operating thermostats (high and low temp selection, presumably), one of them may be bad. If you normally run on high, try low to see if it works then.

If it doesn't work on either, then the heating element may be partially failed such that it isn't producing enough heat to reach the target temperatures.

Or there's a problem with the timer related to internal contacts for the auto-dry function.

Or the exhaust ducting is clogged and you've not yet found where.