In roast every week on a 12kg drum roaster with a friend and i have found now that the weather is getting cool that there is more condensation....this drips down the front of the roaster from the ejection flap.
I have also found the same thing with my Hottop at home. A lot more condensation on the rear filter and the odd drip down the rear leg?
Im not sure exactly whay your roaster is doing this but maybe my similar experiences will ease your mind a little?
From what u describe though... its much worse! And yeas it is feasable that the chaff is blocking some of the airflow?
Is there a difference in profiles between the first, second and third roasts? And what size is the roaster in question?