I have had spider web get in there and cause problems ...
I always cleaned out. With a shotgun mop ...clean ....sprinkled down good with graphite powder .... Cleaned out then problems....added a slick coat for the already coated powders ....
I haven't had powder do it, but shot does it all the time in the .410. I keep a small jewelers type hammer with rubber head on it to tap on the tube before I pull the handle all the way up after dropping the shot. Odd that powder would stick, that tube is pretty big compared to some powder drop tubes on metallic presses. You don't reckon you have a humidity problem?? May need to clean the drop tube, maybe lube with some graphite??