VERY odd soot pattern in Trio combustion chamber

Have a 4 year old Trio with a Carlin EZ conversion gas burner. Flame outs from a dirty flame sensor and an overdue servicing led to opening the chamber. Very heavy black soot, but look at the pattern in the photo of the main chamber. Soot left, NO soot right. What could have caused that pattern??

After cleaning, the tech had to change all 3 adjustments to get it back into spec. Some were off a lot. Something happened. Any quess as to some root causes to check?

Thanks