Even though it's an inconvenience, shipping the unit back so that Rec Tec can identify the substance might be the prudent and safe thing to do. For you and other Rec Tec customers.
I have no affiliation with Rec Tec but as a manufacturer I sure like to be giving advice and service...remember these guys do this for a living
Personally I tend to agree I think the smoke exits too fast and pellets & cookers just aren't designed to be stick burners. Thx again.