Occasionlly (once or twice per week), when gas is called for, 5 of the 6 inshot burners ignite, but the 6th, containing the flame sensor will not ignite. This causes the gas to shut off and then the unit recycles sometimes igniting properly and sometime going into system lockout after 3 tries

Classic case of a dirty cross igniter bar. Many time you can blow out the burner assembly with compressed air to fix the problem. Sometimes you have to remove the burner assembly and physically clean the cross igniter bar/channel. If the compressed air doesn't do it, I would suggest having a tech in to check gas pressures, remove burner assembly, and otherwise service the furnace.