Check all connections for tight contact. make sure there is a complete path to ground. Clean the sensor so it is smooth. As long as a spark appears, it can light a flame as a spark is well over the ignition temperature. Make sure all the ignition parts are in the proper engineered location and the gaps are to specification. After that, the ignition works.
Electronic ignitions are sensitive to chemicals in the air, especially laundry chemicals. They coat the sensors.
Lennox parts are available from Lennox dealers who get them from Lennox warehouses in the region.