Morning all - thanks @Kvangels for digging into this and @nrdlnd & @nhsnielsen for your interest in this.
For the Filter roast recipe on the Esperanca Brazilian coffee, we’ve found that the airflow is very borderline. When we roast these beans, they slow down as the air flow drops off, although for us they’ve not actually stopped moving and sat still. As you’ve speculated, there are probably environmental factors that may make them not move at all, or move just enough - but lesson learnt that we should not sail so close to the wind on our recommended recipes.
If you experience the challenges with beans not moving, there are two solutions; give the roaster a bit of a nudge which can jolt the beans into rotating slowly again, and next roast turn up the airflow by 5-10%.
Wider insight - if you keep the same temperature curve, but change the airflow significantly, it will have a noticeable effect on the roast. Lower airflow tends to make for a slightly darker roast. When the beans are moving slowly as they do on this Brazilian roast recipe, you get more conductive heat transfer between the beans, as well as the convective heat transfer - but on an IKAWA it’s important the beans don’t just sit still for long.