Hi Smitty, I wonder if your shaker linkage, and grate linkage is getting enough wear after the many years, and is getting sloppy enough that you do't have a good control over the grates as you used to have??
Because I KNOW you know that when shaking down a fire, you really are not opening up the gap between the grates.. you are just shaking the floor of the fire, just creating a minor 'earthquake' under the coal bed so that the fire will let the ash fall free and through the slots in the grates..
If your grate/shaker linkage is getting sloppy, you may be opening up the gap wider than you think.
If your grates were covered with a layer of stone from the coal.. then maybe you would jam the grates??
OR,, maybe you need to shake the stove BEFORE you drink the third pot of coffee or ??? Maybe a little less 'energy' in the shaking action..??
AS for the changing of the quality of the coal.. I'm surprised, I've been through the Blaschak breaker,, they do an amazing job of separating out the crap from the coal,, and I've been through the bagging plant.. Blaschak wanted me to become a coal dealer in Michigan.. so I got the whole tour.
In coal mines, if the coal is from underground, or the surface mining has gone deep enough that they have dug into old mines, there is wood from the old bracing that gets into the coal.. and most of this is separtated..
My worst experiences with bagged coall was with Reading.. Pieces of water logged wood the size of a sub-sandwich, in bags of nut.. and a gallon bucket of wet fines to balance out the wood..
. That was the worst bagged crap I've ever bought..
Coal does change in quality, the veins of coal change as they get mined out, and the mines have to move on into new veins.. It's always changing.