Roasting this Nicaraguan Geisha and it’s FC comes soooooo early. I know it’s not misreadings by the Bullet because the IBTS and BT Probe track really nicely and there’s no significant variation to cause concerns. FC was ROLLING around 195C but started around 192/193C. I’ve never had a bean hit FC this early before. Just curious to see if anyone else has? Beautiful roast curve too 
Yep, that does seem early! I have no experience with that bean.
One thing Aillio mentions in their docs is that FC “drifts lower” as the IBTS sensor gets dirty. I suppose a stray piece of chaff could be stuck on it too?
But if you don’t see this kind of drift with other coffees (that is, your current FC temps are otherwise normal) then I would think it’s the bean.
Curious to hear what others say.
I wanted to say it’s probably normal for highly processed Geshas, but then I saw that yours is washed. So I checked your other roasts, and between all the beans cracking around 195-196, adding that the crossover between BT and IBTS happens far too soon, my money is on a dirty IBTS.