Dometic stove

We have the exact same issue. On ours it's the front center burner. I'm going to take a look at it today and see if I can find the problem but I'm guessing it's the Igniter Electrode that's bad because like your issue, sometimes it works but often times it doesn't.

Update: I took the stove top off and used the spark igniter when I had a good look. It worked fine but the burner wouldn't light. So I took it apart, checked to make sure everything was clean and nothing was clogged up and put it back together. Now I can't get it to fail. :h