Which is bad: pilot sensor or igniter/lockout control?

Two parts remain as suspects in an intermittent and rare main burner stoppage before the thermostat is satisfied. It's either the igniter/lockout control or the 3-wire pilot sensor. The pilot remains on after the main burner stops. (Then the furnace shuts down normally, and restarts immediately.) Any strong hunches? Please share! Time between hiccups is about 2.5 days. Thank you, Herb
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