BuffettFan
is Blowin Smoke!
This problem will occur when the tank is shut off before shutting the burners off.
I've had this on my 36 once.
Ran out of gas during a cook, swapped tanks with the BS valves all open.
Turned off all the valves, tank included, then opened the tank and then the BS valves one at a time, slowly.
If not this, then the regulator is the next suspect.