Burner Ignition Problems

Hello again,
I have a continuing problem with my thermador gps366s 6 burner cooktop.

I had poor ingition on 2 burners, replaced the ingitors and they worked better for a while. One rarely works now and the other works cold but usually not after it’s gotten hot and been turned off, no re-ignition. I can of course light these 2 manually.

The extra-low burner does not work at all, no gas when turned on. I know there is a module in the bottom of the unit that all of the ignitors connect and wonder if this has failed? That makes me wonder how this stove works so any insight on that would be helpful as well. How does it recognize ignition etc

My final problem is with "flame noise" at full on. There is a lot of noise from what I would call fliclering of the gas coming out of the burner holes. This also seems to go away once the burner is hot. I am running propane (with the correct orifices replaced) and wonder if the pressure regulator is off?

this site has been a great help, so thanks in advance

regards, Richard