One igniter stopped working on my Thermador cooktop

Igniter on the right front burner stopped working.
When a knob controlling the right front burner is turned, the gas is flowing, but there is no spark.
On the other hand, when any of the other knobs on the control panel are turned, the sparks come out from all igniters (as it is supposed to be). So nothing is wrong with spark itself. Any help with pointing out the problem?
Thanks…