Thermador gas cooktop low simmer burners shut off after normal burners switch ON

Hello, we have a thermador cooktop that has 4 burners; 2 regular and 2 low simmer. We are having issues with the low simmer burners shutting off immediately after any one of the regular burners coming on. If we have the regular one ON and then turn ON the low simmer they all stay ON. But as soon as we shut off the regular and turn them back ON while the low simmer burners are ON the low simmer burners immediately turn OFF. Basically if we need to turn all the burners ON or a combination of low simmer and normal burners the only way to keep them all ON is to turn the normal burners and then after that turn the low simmer. But still if for any reason a normal burn is lit during the low simmer operation the low simmer shuts off. What is the issue? Would someone help. Thanks

Thermador gas cooktop low simmer burners shut off after normal burners switch ON