Apparently this is a problem across brands, so much so that Yoder includes the following in their user manual:
Inspect and clean the pellet hopper area. The interior hopper surface can be wiped down using warm water and detergent. To protect the surface, and promote smooth pellet feeding, coat the surface with car wax.
I suspect there are a number of variables that don't always make themselves obvious. So, just to add some additional experience to this thread here's a pic of my 590 yesterday. I had gotten down to the end of a bin full of Smokehouse Blend (same ones you use Dave) and wanted to reload with the Cookin' Pellets Blend for a rib cook. The Smokehouse dropped in the bin fairly similarly to the experience yesterday in the pic with the CP blend. I don't wax my bin, occasionally wipe out the dust, but that's it. This amount of slump pictured is at the end of a 3.5 hour cook. I'm wondering if it's a function of the wood species rather than a brand.
I did a brisket the other day... a big'un. 17.5 pounds pre-trim. I had some issues with temp moving around a bit more than I would like during first 1.5 hours or so. I adjusted the pellet feed rate from its initial setting down to a 3.
Opened cooker at brisket internal temp of 150 to crutch it... left it till internal of 200. Total cook time was 21 hours. Never had any more issues with temp moving around, it was dead on steady... or pellet issues in the hopper. I'm using the Rec Tec blend pellets that came with my 590. My understanding is that they are the same as Cooking Pellets, just relabeled. I liked them... they came to me nice and dry... I store my pellets in 5 gal white food safe buckets from Lowe's to keep em that way.
Maybe it was the type of wood in the pellet(s) dsandersus? Was it fruit wood? Maybe you had a tiny bit of moisture in your hopper, or slightly damp pellets?
So, I've ran two brands of pellets since purchase - Smokehouse (Sam's Club) and Cooking Pellets. All problems with pellets not feeding (falling into the auger) correctly have occurred while using the CP brand. Hickory, Black Cherry and Apple Mash (Black Cherry was the least problematic). The pellets stick to the outer edge of the hopper and not fall into the auger and subsequently run dry / empty, this has happened twice with CPs.
@Knuckler73 Moisture, I suppose that could be a culprit if the pellets were not handled correctly during packaging. From a hopper perspective considering where I reside, I somehow doubt it as it's pretty darn dry here in Nevada this time of year.
I've given the CP rep. that I purchased the pellets from my feedback and his only comment was "Out of 6 pallets sold you're the only one that has reported this issue, but I will follow up with my rep. and let them know". This is in my opinion the nice way of saying "There is nothing wrong with the pellets and you're just complaining". Maybe i'm just too cynical...
Anyhow, once I switch back to using SH all things work as intended, where the pellets sacrifice themselves to the BBQ fire gods and continue to fuel my cooks.