A spider made its web in the burner orifice
I've seen this numerous times over 30 years in the propane industry
You'll need to remove the orifice and physically remove web
blowing air through the manifold tube won't work,1/2" box wrench is all you'll need
As for the soot, use vinegar and water,it won't completely remove it but a Majority.
Soot is the devils paint!!!