I roast Chiapas often on our 1KG and haven't seen any smoke in the tray. I would check the airflow and make sure you don't have a restriction somewhere within the chimney. Also if your doing a darker roast it might require a higher fan setting in the end but just be careful not to stall your roast. Cheers

If you're seeing smoke/steam from the cooling tray while it's actively cooling (fan is drafting down and out of the tray) you have an airflow issue. I'm surprised it's only happening with one bean but that could have to do with finish temp, density, or something else.

I'd be sure to clean out under your cooling tray if you haven't, remove the tray itself and be sure it's cleaned and all the holes are unblocked.

Open the vent coming off that cooling fan and check for debris/buildup.

Be sure you have positive pressure on your pressure monitor on the front of the drum as well. It's possible you have an issue further up the vent stack but if you're not seeing smoke/steam during the roast, it's likely just your cooling tray that needs to be cleaned.