Big E auger

I've been burning for about 4 years now and had a problem happen last night I've never had before. I'm using MWP softwoods and basically about 1/2 way up the auger the pellets just packed themselves together so nothing would move any more.

I emptied it out and cleared the jam and everything is running fine now but wondering if anyone know why this would have happened?

It was a combination of both made up of short pellets (only 1/4 - 1/2 in length) and fines. I've never had a problem with the fines but I have noticed the MWP softwood do have more than I've used before.