I highly doubt it’s got anything to do with the type of pellets. My 780 works great with any kind. I’m new to pellet grills but from being on here and the information I’ve read, Traeger definitely has a lot of issues and seems to be getting worse. Mine was gifted to me so I’m using it until it quits. But my next one won’t be a Traeger if I pay for it, hopefully my 780 continues to not let me down for a while. I clean it after every use doesn’t matter if it’s a 2 hour cook or 16. It sits outside under a roof with partially open sides and a blowing rain can make contact with it sometimes. I keep pellets in the hopper all the time and I keep it unplugged until I use it. I’m not advertising other brands on here but a few great grills can be found when compared to the price of the Timberlines.
One suggestion, have you tried blowing out the auger chute to make sure nothing is sticking inside it. Periodically I’ll let my 780 run out of pellets when hopper is low. I use my air compressor and blow it out.