The right front burner igniter does not always spark using the right front switch. However, it sparks when lighting off any of the other three burners. Is it the RF switch or spark module? I wouldn't think it's the igniter as it does spark.
The most likely cause for the unit not to spark when using the right front switch would most likely be the switch itself. You can check the ignition switch for continuity when turned to the lite position. If there is no continuity then the switch would need to be changed.