Brett, I believe I have just been down a similar path. After a period of very consistent results, I started to get uneven roasts where some beans were pale and others very shiny. In my case it was carelessness arising in changing the BBQ configuration to cook food and coffee. I have a 3 burner jobbie. To roast coffee I remove the grill and hot-plate and centre the diffuser plate under the drum over the centre and right burners. Previously I have kept the left burner going after the initial heat-up but turner right down. My problems were caused by not repositioning the difusser and having too much heat from the left burner. Fix and it was back to even roasts.
Keep the bulletins going. Hopefully it will get more people realising BBQ roasting is relatively easy and produces great results when you have it nailed.