I'm thinking you hit probably 80% or more of your problem here. If the smoke is trapped, this isn't good. White, heavy grey, in essence could/would be billowy, not good. Trapped; worse. I think you have a very bad burning fire in there that is producing creosote, of which it's accumulating on the meat. Black, over-smoked, bitter, and yes, burned tasting meat can be a result.
Perhaps the wood this time was cold going in (that doesn't help); perhaps it had more moisture than before (this too doesn't help).
Hance - Lake Dogs Cooking Team - MiM/MBN/GBA CBJ and comp cook
Lake Sinclair, GA (strategically about an hour from everywhere)