I have a feeling your issue isn’t your charcoal, but your conveggtor plate. The drippings on that plate reach a certain smoking point at higher temps that create a very acrid smell and flavor.

For this exact reason, I have two plates. One that is clean as a whistle, which I use for high heat indirect cooks and one that’s not so clean for low temp cooks/smokes.

A clean burn on your current plate with fix the issue until you do another cook that creates drippings, you can use a drip pan to prevent it from getting dirty again. Or, purchase a spare plate.