Pyro Cable

[UNG]

Only time I've seen this happen the pot had not been completely filled with compound at the time the only reason I could suggest was condensation had formed in the air pocket thus causing a short

 

[whats an rb4]

i would go for air pocket try as you might ya never really knw if it full

 

[Knobhead]

A small void in the compound. Aluminium oxide is a sod for drawing in moisture.