I noticed my IBTS temperature seems low compared to the first few seasoning roasts, I roast to 2c so thought I’d check the sensor but it looks clean. Will get a cotton bud anyway, but the actual sensor is like a mirror!
Don’t know if this has anything to do with it, but when I did my seasoning roasts on my R2 Pro I was using some Robusta beans and it seemed like my IBTS temps were rather uneven. After I moved on to some Ethiopian beans the temp tracked better. I went back to the Robustas to try an actual roast and my temp line tracked erratically again. In my case the Robusta beans seemed to be the culprit as I have not had that problem since abandoning them. Yours may be a totally different problem.